Implement matrixCompMult in SPIR-V backend

Bug: skia:10913
Change-Id: I59f5b0fb2d015f8543b4038c2c5b18ce24c194a8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/347956
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed