[MP] Let MultiplayerAPI handle packet relaying and peer signaling.

MultiplayerPeer changes:

- Adds is_server_relay_supported virtual method

Informs the upper MultiplayerAPI layer if it can signal peers connected
to the server to other clients, and perform packet relaying among them.

- Adds get_packet_channel and get_packet_mode virtual methods

Allows the MultiplayerAPI to retrieve the channel and transfer modes to
use when relaying the last received packet.

SceneMultiplayerPeer changes:

- Implement peer signaling and packet relaying when the MultiplayerPeer
  advertise they are supported.

ENet, WebRTC, WebSocket changes:

- Removed custom code for relaying from WebSocket and ENet, and let it
  be handled by the upper layer.
- Update WebRTC to split create_client, create_server, and create_mesh,
  with the latter behaving like the old initialize with
  "server_compatibility = false", and the first two supporting the upper
  layer relaying protocol.

1 files changed, 2 insertions, 4 deletions

diff --git a/modules/multiplayer/scene_cache_interface.cpp b/modules/multiplayer/scene_cache_interface.cpp
index b3b642f815..7df9b95b30 100644
--- a/modules/multiplayer/scene_cache_interface.cpp
+++ b/modules/multiplayer/scene_cache_interface.cpp
@@ -105,8 +105,7 @@ void SceneCacheInterface::process_simplify_path(int p_from, const uint8_t *p_pac
 
 	multiplayer_peer->set_transfer_channel(0);
 	multiplayer_peer->set_transfer_mode(MultiplayerPeer::TRANSFER_MODE_RELIABLE);
-	multiplayer_peer->set_target_peer(p_from);
-	multiplayer_peer->put_packet(packet.ptr(), packet.size());
+	multiplayer->send_command(p_from, packet.ptr(), packet.size());
 }
 
 void SceneCacheInterface::process_confirm_path(int p_from, const uint8_t *p_packet, int p_packet_len) {
@@ -162,10 +161,9 @@ Error SceneCacheInterface::_send_confirm_path(Node *p_node, NodePath p_path, Pat
 
 	Error err = OK;
 	for (int peer_id : p_peers) {
-		multiplayer_peer->set_target_peer(peer_id);
 		multiplayer_peer->set_transfer_channel(0);
 		multiplayer_peer->set_transfer_mode(MultiplayerPeer::TRANSFER_MODE_RELIABLE);
-		err = multiplayer_peer->put_packet(packet.ptr(), packet.size());
+		err = multiplayer->send_command(peer_id, packet.ptr(), packet.size());
 		ERR_FAIL_COND_V(err != OK, err);
 		// Insert into confirmed, but as false since it was not confirmed.
 		psc->confirmed_peers.insert(peer_id, false);