Support for 3D sync to physics

[pouleyKetchoupp]

Same implementation as in 2D, based on the code from PR #49327.

Closes godotengine/godot-proposals#961.
Fixes #36334

[pouleyKetchoupp]

I've just pushed an extra modification in move_and_slide that can help with moving platforms, the same one that's already done in 2D:

godot/scene/2d/physics_body_2d.cpp

Lines 925 to 932 in 090e4c4

	Vector2 current_floor_velocity = floor_velocity;
	if (on_floor && on_floor_body.is_valid()) {
	//this approach makes sure there is less delay between the actual body velocity and the one we saved
	PhysicsDirectBodyState2D *bs = PhysicsServer2D::get_singleton()->body_get_direct_state(on_floor_body);
	if (bs) {
	current_floor_velocity = bs->get_linear_velocity();
	}
	}

[akien-mga]

Thanks!