Add a fast codepath for SkPath.addPath(kAppend)

Change-Id: I49469f29cc10032d687b938ded379ef7e2f52da2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/269190
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
3 files changed