Support ES2-compliant for loops in SkSL-to-SkVM

Such loops must be unrollable, so that's what we do.

Bug: skia:11094
Change-Id: I1b34917b6f2d015ae7867415d0120a5df0ffd618
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/353619
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
2 files changed