Fix SwizzleIndexLookup in SkRP codegen.

We can reuse the SPIR-V swizzled-index transformation logic in SkRP.
This gets SwizzleIndexLookup to pass successfully.

Change-Id: Ie2268761719881548d4159b63e61ee9500d5a300
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/656248
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed