Remove animation 3D transform track, replace by loc/rot/scale tracks.

* `Animation.TYPE_TRANSFORM3D` track is gone.
* Added POSITION_3D, ROTATION_3D, SCALE_3D tracks.
* GLTF2, Collada, FBX importers will only import the track types found.
* Skeleton3D bone poses are now Pos/Rot/Scale, pose matrix removed.
* AnimationPlayer and AnimationTree animate these tracks separately, only when found.
* Removed BakeReset code, is useless with these changes.

This is the first in a series of commits designed to make the animation system in Godot more useful, which includes:

* Better compatibility with Autodesk products
* Better reusability of animations across models (including retargeting).
* Proper animation compression.
* etc.

*Note* GLTF2 animation saving went broken with this PR, needs to be fixed in a subsequent one.

3 files changed, 69 insertions, 31 deletions

diff --git a/doc/classes/Animation.xml b/doc/classes/Animation.xml
index d2ecbdde26..a35b784106 100644
--- a/doc/classes/Animation.xml
+++ b/doc/classes/Animation.xml
@@ -253,6 +253,14 @@
 				Returns the arguments values to be called on a method track for a given key in a given track.
 			</description>
 		</method>
+		<method name="position_track_insert_key">
+			<return type="int" />
+			<argument index="0" name="track_idx" type="int" />
+			<argument index="1" name="time" type="float" />
+			<argument index="2" name="position" type="Vector3" />
+			<description>
+			</description>
+		</method>
 		<method name="remove_track">
 			<return type="void" />
 			<argument index="0" name="track_idx" type="int" />
@@ -260,6 +268,22 @@
 				Removes a track by specifying the track index.
 			</description>
 		</method>
+		<method name="rotation_track_insert_key">
+			<return type="int" />
+			<argument index="0" name="track_idx" type="int" />
+			<argument index="1" name="time" type="float" />
+			<argument index="2" name="rotation" type="Quaternion" />
+			<description>
+			</description>
+		</method>
+		<method name="scale_track_insert_key">
+			<return type="int" />
+			<argument index="0" name="track_idx" type="int" />
+			<argument index="1" name="time" type="float" />
+			<argument index="2" name="scale" type="Vector3" />
+			<description>
+			</description>
+		</method>
 		<method name="track_find_key" qualifiers="const">
 			<return type="int" />
 			<argument index="0" name="track_idx" type="int" />
@@ -466,25 +490,6 @@
 				Swaps the track [code]idx[/code]'s index position with the track [code]with_idx[/code].
 			</description>
 		</method>
-		<method name="transform_track_insert_key">
-			<return type="int" />
-			<argument index="0" name="track_idx" type="int" />
-			<argument index="1" name="time" type="float" />
-			<argument index="2" name="location" type="Vector3" />
-			<argument index="3" name="rotation" type="Quaternion" />
-			<argument index="4" name="scale" type="Vector3" />
-			<description>
-				Insert a transform key for a transform track.
-			</description>
-		</method>
-		<method name="transform_track_interpolate" qualifiers="const">
-			<return type="Array" />
-			<argument index="0" name="track_idx" type="int" />
-			<argument index="1" name="time_sec" type="float" />
-			<description>
-				Returns the interpolated value of a transform track at a given time (in seconds). An array consisting of 3 elements: position ([Vector3]), rotation ([Quaternion]) and scale ([Vector3]).
-			</description>
-		</method>
 		<method name="value_track_get_key_indices" qualifiers="const">
 			<return type="PackedInt32Array" />
 			<argument index="0" name="track_idx" type="int" />
@@ -541,19 +546,22 @@
 		<constant name="TYPE_VALUE" value="0" enum="TrackType">
 			Value tracks set values in node properties, but only those which can be Interpolated.
 		</constant>
-		<constant name="TYPE_TRANSFORM3D" value="1" enum="TrackType">
-			Transform3D tracks are used to change node local transforms or skeleton pose bones of 3D nodes. Transitions are interpolated.
+		<constant name="TYPE_POSITION_3D" value="1" enum="TrackType">
+		</constant>
+		<constant name="TYPE_ROTATION_3D" value="2" enum="TrackType">
+		</constant>
+		<constant name="TYPE_SCALE_3D" value="3" enum="TrackType">
 		</constant>
-		<constant name="TYPE_METHOD" value="2" enum="TrackType">
+		<constant name="TYPE_METHOD" value="4" enum="TrackType">
 			Method tracks call functions with given arguments per key.
 		</constant>
-		<constant name="TYPE_BEZIER" value="3" enum="TrackType">
+		<constant name="TYPE_BEZIER" value="5" enum="TrackType">
 			Bezier tracks are used to interpolate a value using custom curves. They can also be used to animate sub-properties of vectors and colors (e.g. alpha value of a [Color]).
 		</constant>
-		<constant name="TYPE_AUDIO" value="4" enum="TrackType">
+		<constant name="TYPE_AUDIO" value="6" enum="TrackType">
 			Audio tracks are used to play an audio stream with either type of [AudioStreamPlayer]. The stream can be trimmed and previewed in the animation.
 		</constant>
-		<constant name="TYPE_ANIMATION" value="5" enum="TrackType">
+		<constant name="TYPE_ANIMATION" value="7" enum="TrackType">
 			Animation tracks play animations in other [AnimationPlayer] nodes.
 		</constant>
 		<constant name="INTERPOLATION_NEAREST" value="0" enum="InterpolationType">
diff --git a/doc/classes/AnimationTree.xml b/doc/classes/AnimationTree.xml
index 3d112e258e..40dcd950d7 100644
--- a/doc/classes/AnimationTree.xml
+++ b/doc/classes/AnimationTree.xml
@@ -22,7 +22,7 @@
 		<method name="get_root_motion_transform" qualifiers="const">
 			<return type="Transform3D" />
 			<description>
-				Retrieve the motion of the [member root_motion_track] as a [Transform3D] that can be used elsewhere. If [member root_motion_track] is not a path to a track of type [constant Animation.TYPE_TRANSFORM3D], returns an identity transformation. See also [member root_motion_track] and [RootMotionView].
+				Retrieve the motion of the [member root_motion_track] as a [Transform3D] that can be used elsewhere. If [member root_motion_track] is not a path to a track of type [constant Animation.TYPE_POSITION_3D], [constant Animation.TYPE_SCALE_3D] or [constant Animation.TYPE_ROTATION_3D], returns an identity transformation. See also [member root_motion_track] and [RootMotionView].
 			</description>
 		</method>
 		<method name="rename_parameter">
@@ -45,7 +45,7 @@
 		</member>
 		<member name="root_motion_track" type="NodePath" setter="set_root_motion_track" getter="get_root_motion_track" default="NodePath(&quot;&quot;)">
 			The path to the Animation track used for root motion. Paths must be valid scene-tree paths to a node, and must be specified starting from the parent node of the node that will reproduce the animation. To specify a track that controls properties or bones, append its name after the path, separated by [code]":"[/code]. For example, [code]"character/skeleton:ankle"[/code] or [code]"character/mesh:transform/local"[/code].
-			If the track has type [constant Animation.TYPE_TRANSFORM3D], the transformation will be cancelled visually, and the animation will appear to stay in place. See also [method get_root_motion_transform] and [RootMotionView].
+			If the track has type [constant Animation.TYPE_POSITION_3D], [constant Animation.TYPE_ROTATION_3D] or [constant Animation.TYPE_SCALE_3D] the transformation will be cancelled visually, and the animation will appear to stay in place. See also [method get_root_motion_transform] and [RootMotionView].
 		</member>
 		<member name="tree_root" type="AnimationNode" setter="set_tree_root" getter="get_tree_root">
 			The root animation node of this [AnimationTree]. See [AnimationNode].
diff --git a/doc/classes/Skeleton3D.xml b/doc/classes/Skeleton3D.xml
index 6ab5ed55a3..e046527b17 100644
--- a/doc/classes/Skeleton3D.xml
+++ b/doc/classes/Skeleton3D.xml
@@ -144,6 +144,24 @@
 				Returns the pose transform of the specified bone. Pose is applied on top of the custom pose, which is applied on top the rest pose.
 			</description>
 		</method>
+		<method name="get_bone_pose_position" qualifiers="const">
+			<return type="Vector3" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+			</description>
+		</method>
+		<method name="get_bone_pose_rotation" qualifiers="const">
+			<return type="Quaternion" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+			</description>
+		</method>
+		<method name="get_bone_pose_scale" qualifiers="const">
+			<return type="Vector3" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+			</description>
+		</method>
 		<method name="get_bone_rest" qualifiers="const">
 			<return type="Transform3D" />
 			<argument index="0" name="bone_idx" type="int" />
@@ -337,13 +355,25 @@
 				[b]Note:[/b] [code]parent_idx[/code] must be less than [code]bone_idx[/code].
 			</description>
 		</method>
-		<method name="set_bone_pose">
+		<method name="set_bone_pose_position">
 			<return type="void" />
 			<argument index="0" name="bone_idx" type="int" />
-			<argument index="1" name="pose" type="Transform3D" />
+			<argument index="1" name="position" type="Vector3" />
+			<description>
+			</description>
+		</method>
+		<method name="set_bone_pose_rotation">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="rotation" type="Quaternion" />
+			<description>
+			</description>
+		</method>
+		<method name="set_bone_pose_scale">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="scale" type="Vector3" />
 			<description>
-				Sets the pose transform for bone [code]bone_idx[/code].
-				[b]Note:[/b] The pose transform needs to be in bone space. Use [method world_transform_to_global_pose] to convert a world transform, like one you can get from a [Node3D], to bone space.
 			</description>
 		</method>
 		<method name="set_bone_rest">