Decouple SPIR-V code generation from SkSL::Compiler.

Bug: b/317363889
Bug: b/40045064
Change-Id: Iab7165323733c079af6fbe779a2361fe526c19e4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/793576
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
7 files changed