[COLRv1] Add tests for PaintColrGlyph cycle detection

Add tests that check whether a PaintColrGlyph cycle causes problems, and
whether PaintColrGlyph paints that are siblings in the tree (not forming
a cycle) paint correctly.

[1] https://github.com/googlefonts/color-fonts/blob/main/glyph_descriptions.md#:~:text=gradient%20alpha%20values.-,176,-%F3%B1%84%80

Change-Id: Iddd0f6ca4924fa1f893c852de912d2dc28bfd7a4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/793476
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Dominik Röttsches <drott@google.com>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
1 file changed