Major rearchitecture of SkSL parsing, focused on improving performance.

Bug: skia:
Change-Id: I83e3a094d26085fc4d586e5d2581e0d61c55634e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/145080
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
75 files changed