This has been superseded by GDExtension so this code is no longer useful
nor usable.
There's still some GDNative-related stuff in platform export code which
needs to be adapted for GDExtension (e.g. to include GDExtension libraries
in exports).
This makes it easier to spot syntax errors when editing the
class reference. The schema is referenced locally so validation
can still work offline.
Each class XML's schema conformance is also checked on GitHub Actions.
