Update GrConvexPolyEffect to support an input FP.

Change-Id: I813a4e4a5b4b0dc4f8ea59056d125386e6049ab4
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296516
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
6 files changed