-Fixes to undo redo to avoid crash, closes #24251

-Changed Animation to have a special signal when tracks are changed, to avoid unnecesary track cache rebuilds in AnimationPlayer
-Added missing emit_changed whe modifying keys to Animation
-Changed AnimationPlayer to use the new refcounted connections instead of the previous hacky way to keep references
-Changed AnimationEditor to update the current track when keys are edited
-Fixed bug where undo/redo did not work with AnimationKeyEdit (was not being updated)
-Made sure UndoRedo does not mind deleted objects in undo/redo history, this would corrupt the history or clear it without need.

scene/animation/animation_player.h

@@ -181,8 +181,6 @@ private:
 	int cache_update_bezier_size;
 	Set<TrackNodeCache *> playing_caches;
 
-	Map<Ref<Animation>, int> used_anims;
-
 	uint64_t accum_pass;
 	float speed_scale;
 	float default_blend_time;