[coop] Transition various public APIs into an external/internal form to avoid unneces...

[coop] Transition various public APIs into an external/internal form to avoid unnecessary GC-unsafe calls (#14427)

Relevant issue: #14376

There are potentially more functions this can apply to, but this covers the ones listed in the issue and an extra one I found in the process.

Functions were either broken off into an external-only and internal version, or such a pair already existed and the internal version was moved from the source file to a separate `-internals` header, similarly to in 3c74df566776f468366d96dd164dd1a6b3d780cc.

This gets slightly complicated with `mono_domain_set` and `mono_domain_set_internal`, both of which are currently public (thanks to 4beada28924879ede55f3bf8b3f5b798d0f4637e) and have different signatures. Additionally, the latter does not actually include the gc-unsafe transition despite being public.
I've opted to introduce `mono_domain_set_fast` as the 'internal' version of `mono_domain_set`, to add the proper gc-unsafe transition to `mono_domain_set_internal`, and then to migrate internal usage to `mono_domain_set_internal_with_options`. As part of that I've marked `mono_domain_set_internal` as external only, which is unfortunate naming-wise but I believe the best option here without introducing API breakage.