Add int-vector folding tests to VectorFolding.

This test is meant to demonstrate that constant folding for int and
float vectors is not on equal footing. Float vectors currently generate
better-optimized output.

Change-Id: Ib4822c7b594e9bc4eb4fb9cfe6ab46f7f76268d6
Bug: skia:10908
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332423
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed