Decouple WGSL code generation from SkSL::Compiler.

Bug: b/317363889
Bug: b/40045064
Change-Id: Idef8045eeaee3d94306773ed14615d8f58867604
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/793317
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
7 files changed