microsoft/compiler: Lower fquantize2f16

microsoft/compiler: Lower fquantize2f16

As far as I can't tell, there's no native operation doing this
equivalent of fquantize2f16. Let's lower this operation to

   if (val < MIN_FLOAT16)
      return -INFINITY;
   else if (val > MAX_FLOAT16)
      return -INFINITY;
   else if (fabs(val) < SMALLER_NORMALIZED_FLOAT16)
      return 0;
   else
      return val;

which matches the definition of OpQuantizeToF16:

"
If Value is an infinity, the result is the same infinity.
If Value is a NaN, the result is a NaN, but not necessarily the same NaN.
If Value is positive with a magnitude too large to represent as a 16-bit
floating-point value, the result is positive infinity. If Value is negative
with a magnitude too large to represent as a 16-bit floating-point value,
the result is negative infinity. If the magnitude of Value is too small to
represent as a normalized 16-bit floating-point value, the result may be
either +0 or -0.
"

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16959>