Add a dedicated Op for analytic round rects

Adds a GrAAFillRRectOp class that can draw any round rect, including
complex. The Op makes use of instanced rendering and fwidth().

Bug: chromium:860021
Change-Id: I3d8818a003899b56c33d35babe22cd15d3f8e110
Reviewed-on: https://skia-review.googlesource.com/c/170729
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
9 files changed