Make Comparator& refs in GrTriangulator const

TBR=jvanverth@google.com

Bug: skia:10419
Change-Id: I6da265e732b5588e1780da8b509d21ce65746a5a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/351796
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed