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/nir.h

@@ -2950,6 +2950,7 @@ void nir_lower_alpha_test(nir_shader *shader, enum compare_func func,
                           bool alpha_to_one);
 bool nir_lower_alu(nir_shader *shader);
 bool nir_lower_alu_to_scalar(nir_shader *shader);
+bool nir_lower_bool_to_float(nir_shader *shader);
 bool nir_lower_bool_to_int32(nir_shader *shader);
 bool nir_lower_load_const_to_scalar(nir_shader *shader);
 bool nir_lower_read_invocation_to_scalar(nir_shader *shader);