Have GrFillRRectOp make use of the GrSimpleMeshDrawOpHelper

I'm not sure why this wasn't converted to using a GrSMDOH earlier.

Change-Id: Ie8b0e2ce3787dfef4459524eec671d769cacdb5a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/278465
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed