added support for half input variables in SkSL fragment processors

Bug: skia:
Change-Id: Iccdd98d9949c2a5f3da650282f520c65f2bb5094
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205350
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Jonathan Backer <backer@chromium.org>
5 files changed