nir: Rework the way samplers are lowered
nir: Rework the way samplers are lowered

v2 Jason Ekstrand <jason.ekstrand@intel.com>:
 - Use the nir_tex_src_sampler_offset source type instead of the
   sampler_indirect thing that I cooked up before.

Reviewed-by: Chris Forbes <5dcac483e7a6e31a5cbe89f38cc69dff8ee93dac@ijw.co.nz>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler