Move init code from pipeline stage generator to GrSkSLFP

Having the logic to emit, parse, and re-emit this boilerplate spread
across the generator and FP was unnecessary. Having it emitted directly
is simpler, and will allow some flexibility when we change the signature
of runtime effect SkSL.

Change-Id: I7ebd5e62bfe1e41035c4fb9efadb427be915b9f8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310158
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed