Implement compile-time optimization for clamp().

$genType clamp($genType x, $genType minVal, $genType maxVal);
$genType clamp($genType x, float minVal, float maxVal);
$genHType clamp($genHType x, $genHType minVal, $genHType maxVal);
$genHType clamp($genHType x, half minVal, half maxVal);
$genIType clamp($genIType x, $genIType minVal, $genIType maxVal);
$genIType clamp($genIType x, int minVal, int maxVal);

Change-Id: I726270e84fca781825e59abed0c8c7d099ca7444
Bug: skia:12034
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/411839
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
9 files changed