Support global variables in pipeline stage generator

Bug: skia:11295
Change-Id: Iec11f3f4d26eb5b1c07707b3cedd09096bad80d0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/371478
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
6 files changed