Remove the offthread triangulation from GrPathTessellateOp

Rather than copying these triangles twice, we can run "pathToPolys"
during onPrePrepare and "polysToTriangles" during onPrepare.

Also adds a benchmark for normal and inner-fan triangulation.

Bug: skia:10419
Change-Id: Id301afde5de11d93ae026e75e42ac03a50867687
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/355177
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
8 files changed