Use pathbuilder to keep path immutable

Change-Id: I1116a203d28a530dfda590964e5ce54bcaf1876f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1056716
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Commit-Queue: Mike Reed <mike@reedtribe.org>
Reviewed-by: Florin Malita <fmalita@google.com>
14 files changed