Add API for glyph image data

Move the invariants for glyph image data into SkGlyph.

Change-Id: I1958612bb73cfffe42df19a11c8899048559013b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/222876
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
12 files changed