Input event type for mouse button events.
Contains mouse click information. See [method Node._input].
http://docs.godotengine.org/en/3.0/tutorials/inputs/mouse_and_input_coordinates.html
Mouse button identifier, one of the BUTTON_* or BUTTON_WHEEL_* constants in [@GlobalScope].
If [code]true[/code] the mouse button's state is a double-click. If [code]false[/code] the mouse button's state is released.
Magnitude. Amount (or delta) of the event. Used for scroll events, indicates scroll amount (vertically or horizontally). Only supported on some platforms, sensitivity varies by platform. May be 0 if not supported.
If [code]true[/code] the mouse button's state is pressed. If [code]false[/code] the mouse button's state is released.