nir: Add a bool to float32 lowering pass

From @jekstrand's nir-1-bit-bool branch, with improved ior/inot lowering.

ior: fmax instead of fadd allows removing the fsat.

inot: seq(x, 0) can be better than fsub(1, x). On a2xx, it works better
with the scalar instruction set.

Reviewed-by: Jonathan Marek <jonathan@marek.ca>

src/compiler/nir/meson.build

@@ -114,6 +114,7 @@ files_libnir = files(
   'nir_lower_alpha_test.c',
   'nir_lower_atomics_to_ssbo.c',
   'nir_lower_bitmap.c',
+  'nir_lower_bool_to_float.c',
   'nir_lower_bool_to_int32.c',
   'nir_lower_clamp_color_outputs.c',
   'nir_lower_clip.c',