Simplify some RP data layout and logic

- Remove lazy evaluation from the Ctx struct. It's always evaluated
  exactly once, so this was doing nothing.
- Always include a context pointer for each stage (except the final
  return). This is going to make relative branches possibly without
  pessimizing the stage function signature.

Change-Id: I4697e96a8d8ec6fe31d93b013939a9d811c73b39
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/566339
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed