SkAdvancedTypefaceMetrics: factor out GlyphToUnicode

Change-Id: Iedce8c1ea2c405d5ab64ccac353970d5cd2b9d63
Reviewed-on: https://skia-review.googlesource.com/126507
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
25 files changed