cleaned up SkSL constant handling

Bug: skia:
Change-Id: I8131c4348f0f91bc2705e493918c4ca2d1f4867b
Reviewed-on: https://skia-review.googlesource.com/95920
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
5 files changed