This commit adds the classes OpenXRExtensionWrapperExtension and OpenXRAPIExtension
that can be used in GDExtensions to define OpenXR extension wrappers.
It modifies extension wrapper registration so that they can be registered
before OpenXRAPI instantiation (e.g. in core level initialization of GDExtensions).
Developed by Migeran (https://migeran.com)
Gabor Koncz