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

(cherry picked from commit 86fd40b06c14f32327def8d872312974ecd32436)

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();