In GrSkSLFP, store inputs as SkData. Tighten size checks.

Simplifies interaction with users who already have inputs in this form,
and doesn't really add any overhead to other clients.

Change-Id: I6e137e02a65e007621adf481ffb994665117caf4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268836
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
9 files changed