mesa/main/pack_tmp.h: Add float conversion support
mesa/main/pack_tmp.h: Add float conversion support

We will use this in a later patch to refactor _mesa_pack_rgba_span_float.

Signed-off-by: Samuel Iglesias Gonsalvez <b753b212f30aed827c3eea2e437609dc37310153@igalia.com>
Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler