microsoft/compiler: Simplify nir_intrinsic_load_front_face handling

microsoft/compiler: Simplify nir_intrinsic_load_front_face handling

It is invalid to have Boolean variables as either shader inputs or
outputs, so there is no point to try to lower them in general.  The only
use for this was some two-phase lowering of
nir_intrinsic_load_front_face that could be done in a single phase.
Create the SYSTEM_VALUE_FRONT_FACE as a uint and compare it with zero at
the same time.

No shader-db or fossil-db changes on any Intel platform.

v2: Remove dxil_nir_lower_bool_input from dxil_nir.h and drop it from
the other caller in the spirv_to_dxil codepath.  Noticed by Jesse.  Fix
setting bit size when loading SYSTEM_VALUE_FRONT_FACE.  Caught by CI.

v3: Use nir_ine_imm.  Change type of gl_FrontFacing GS output in
d3d12_nir_passes from Boolean to integer.  Both suggested by Jesse.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15121>