Mangle function names in SPIR-V.

SPIR-V doesn't seem to mind overlapping function names, since they're
not load-bearing in any way, but this keeps us consistent with the other
code generators.

Change-Id: Ifdb4cb17795da88eabc0db841af746fb76caf423
Bug: skia:10851
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/387757
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
87 files changed