Replace getVecComponent with getConstantSubexpression.

Change-Id: I792f23d3aba45bdaea174ee51d4aca5bd9cb4ea4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/393079
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
10 files changed