Only show AnimationEditor automatically when an Animplayer is selected.

Previous behaviour was to show it when an AnimationPlayer has been detected in the scene, now you actually have to select it.
Fixes #6213

tools/editor/plugins/animation_player_editor_plugin.cpp

@@ -666,7 +666,7 @@ void AnimationPlayerEditor::set_state(const Dictionary& p_state) {
 			return;
 
 		Node *n = EditorNode::get_singleton()->get_edited_scene()->get_node(p_state["player"]);
-		if (n && n->cast_to<AnimationPlayer>()) {
+		if (n && n->cast_to<AnimationPlayer>() && EditorNode::get_singleton()->get_editor_selection()->is_selected(n)) {
 			player=n->cast_to<AnimationPlayer>();
 			_update_player();
 			show();