Implement compile-time optimization for faceforward().

This implementation leans heavily into DSL. I also reworked the
`normalize` intrinsic to use more DSL to shrink the implementation.

$genType faceforward($genType N, $genType I, $genType Nref);
$genHType faceforward($genHType N, $genHType I, $genHType Nref);

Change-Id: I73ab11d3fe449d2f2c0ae0d745fc39824fc64771
Bug: skia:12034
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/412637
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>
5 files changed