Fix Variant Ref<> assignment.

-Creating from object pointer via funcptr API was missing reference initialization.
-Supersedes https://github.com/godotengine/godot-cpp/pull/662
-Fixes several crashes in GDExtension

core/variant/variant.cpp

@@ -1023,6 +1023,13 @@ bool Variant::is_null() const {
 	}
 }
 
+bool Variant::initialize_ref(Object *p_object) {
+	RefCounted *ref_counted = const_cast<RefCounted *>(static_cast<const RefCounted *>(p_object));
+	if (!ref_counted->init_ref()) {
+		return false;
+	}
+	return true;
+}
 void Variant::reference(const Variant &p_variant) {
 	switch (type) {
 		case NIL: