[graphite] Start fleshing out AnalyticRRectRenderStep

Change-Id: I9132ae54b970cdf12126c2e8ee3caf942fe315f0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/575978
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
3 files changed