Make `property_list_changed_notify` protected in `Object`

Alternative to `_change_notify()` to be called from within C++ classes.

Achieves low-level consistency with scripting, where this method is
exposed for updating the editor (inspector) with new values.

(cherry picked from commit 9aa06c3e65c6b760422da027d4913aa89c4f39d1)

core/object.h

@@ -511,8 +511,6 @@ private:
 	void _set_indexed_bind(const NodePath &p_name, const Variant &p_value);
 	Variant _get_indexed_bind(const NodePath &p_name) const;
 
-	void property_list_changed_notify();
-
 	friend class Reference;
 	uint32_t instance_binding_count;
 	void *_script_instance_bindings[MAX_SCRIPT_INSTANCE_BINDINGS];
@@ -551,6 +549,7 @@ protected:
 
 	void cancel_delete();
 
+	void property_list_changed_notify();
 	virtual void _changed_callback(Object *p_changed, const char *p_prop);
 
 	//Variant _call_bind(const StringName& p_name, const Variant& p_arg1 = Variant(), const Variant& p_arg2 = Variant(), const Variant& p_arg3 = Variant(), const Variant& p_arg4 = Variant());