docs/nir: use hawkmoth instead of doxygen

Use the hawkmoth c:auto* directives to incorporate nir documentation.

Convert @param style parameter descriptions to rst info field lists.
Add static stubs for generated headers. Fix a lot of references, in
particular the symbols are now in the Sphinx C domain, not C++
domain. Tweak syntax here and there.

Based on the earlier work by Erik Faye-Lund <kusmabite@gmail.com>

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24507>

docs/conf.py

@@ -224,6 +224,7 @@ hawkmoth_clang = [
   '-Idocs/header-stubs/',
   '-Iinclude/',
   '-Isrc/',
+  '-Isrc/gallium/include/',
   '-DHAVE_STRUCT_TIMESPEC',
   '-DHAVE_PTHREAD',
   '-DHAVE_ENDIAN_H',