Apply RTFlip to the sk_FragCoord without using DSL.

As before, this generates slightly different (and tighter) SPIR-V
output, but it is functionally the same.

Change-Id: I43e25df28426ce74ff0bc02cffd044e7d88dd842
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/695960
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Arman Uguray <armansito@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
4 files changed