[graphite] Add SkTileModeToStr

This is to be used in the PaintParamKey's block dumping methods.

Bug: skia:12701
Change-Id: I14de21d2d8b30e0fa69ac2e33fa975dc20f6656c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/493217
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed