[sksl][wgsl] Introduce SkSLWGSLCodeGenerator

Introduce a new WGSL codegen backend. It currently only supports
fragment/vertex stage input and output variable declarations.

Bug: skia:13092
Change-Id: If9e4e432794eb95fd33719be5c0141dfc2cb5680
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/526757
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Arman Uguray <armansito@google.com>
4 files changed