Add More Annotations to GDScript

[JustDooooIt]

GDScript currently has limited static checks. We should introduce annotations like Dart's meta, such as:

@mustCallSuper (mandatory parent call)
@Protected (function visibility)

[dalexeev]

• See Reimplement soft access restriction for members prefixed with _ #103768.

We don't want to introduce keywords/annotations without runtime guarantees that are difficult to implement without a performance penalty and properly due to the way Godot works (set(), get(), call() are core APIs, not GDScript).