meta: Rename the "sampler" stuff to "blit shader".

meta: Rename the "sampler" stuff to "blit shader".

While these structs are generated per GLSL sampler type, they're structs
of data-about-shaders (notably, the ID of a shader program), not
data-about-samplers.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>