rusticl: add proc macro module for generating API stubs

rusticl: add proc macro module for generating API stubs

Most of the API stubs are very very trivial to generate as the sole
purpose of those are to deconstruct the returned `Result` object.

Sadly we can't use external crates yet, so "syn" and "qoute" can't be used
for this :'(

The code is kinda hacky, but we also don't expose this to other people, so
we can keep this as a big hack until we can use external crates.

I wish there was a better solution here.

Signed-off-by: Karol Herbst <git@karolherbst.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23413>