nir: Make boolean conversions sized just like the others

Instead of a single i2b and b2i, we now have i2b32 and b2iN where N is
one if 8, 16, 32, or 64.  This leads to having a few more opcodes but
now everything is consistent and booleans aren't a weird special case
anymore.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/compiler/nir/nir_opt_if.c

@@ -509,7 +509,7 @@ can_propagate_through_alu(nir_src *src)
       case nir_op_ior:
       case nir_op_iand:
       case nir_op_inot:
-      case nir_op_b2i:
+      case nir_op_b2i32:
          return true;
       case nir_op_bcsel:
          return src == &alu->src[0].src;