Add support for "static" method qualifiers

[exigow]

In Godot 3 there was clear distinction between classes (Vector2 ,Node) and singletons (Input) which had only static methods.

Godot 4 introduces static methods for non-singleton classes. It's not supported by plugin.

For example: DirAccess class can be instantiated but also has static methods (like DirAccess.open(dir)). This open(dir) method should be autocompleted in same as Input.is_key_pressed(key).

Additional consideration: Maybe the distinction between singletons and classes is no longer useful?