Migrate gms to use pathbuilder

Change-Id: Ic9b83825d1523f353571cd2224f9595abf69becc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1058616
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Mike Reed <mike@reedtribe.org>