Implement autokeying in Animation editor.

(cherry picked from commit 296c74072c0f4d71567c425a94d9502a68b6e177)

editor/animation_track_editor.cpp

@@ -3540,6 +3540,9 @@ void AnimationTrackEditor::_snap_mode_changed(int p_mode) {
 }
 
 void AnimationTrackEditor::_update_step_spinbox() {
+	if (!animation.is_valid()) {
+		return;
+	}
 	step->set_block_signals(true);
 
 	if (timeline->is_using_fps()) {

editor/plugins/canvas_item_editor_plugin.h

@@ -350,6 +350,7 @@ private:
 	Button *key_rot_button;
 	Button *key_scale_button;
 	Button *key_insert_button;
+	Button *key_auto_insert_button;
 
 	PopupMenu *selection_menu;
 
@@ -421,6 +422,8 @@ private:
 
 	Object *_get_editor_data(Object *p_what);
 
+	void _insert_animation_keys(bool p_location, bool p_rotation, bool p_scale, bool p_on_existing);
+
 	void _keying_changed();
 
 	void _unhandled_key_input(const Ref<InputEvent> &p_ev);