[Tests] Add check for argument name validity

[AThousandShips]

Checks that all method and signal arguments have valid names

See:

• extension_api.json is not sanitized godot-cpp#1536

I'd say a check in unit tests should suffice, but we could add checks in the API dump as well but we'd need to add some more for class, method, and signal names etc., which would double with the unit tests so I'd say the unit tests should cover the API

[AThousandShips]

Will move to the arg check and add the vararg check to prevent issues with empty cases, will push once CI is done

[OffsetMOSFET]

This is a good fix.

I think the only thing that could be added is checking against reserved C++ keywords, but at least those should compile error for godot-cpp.

[AThousandShips]

C++ keywords are already sanitized in godot-cpp:
https://github.com/godotengine/godot-cpp/blob/f2b521f55a0a2ba7080418ba898b97028da6134a/binding_generator.py#L2775-L2795