intel/fs: Introduce lowering pass to implement derivatives in terms of quad swizzles.

intel/fs: Introduce lowering pass to implement derivatives in terms of quad swizzles.

Unfortunately the funky Align1 regions used by the code generator in
order to implement derivatives efficiently aren't available to the
floating-point pipeline on XeHP.  We need to lower them into a number
of pipelined integer shuffle instructions followed by the
floating-point difference computation.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10000>