Introduce SkGlyphDrawableBuffer

Used for efficient glyph id to glyph lookup.

This is part of a larger change:
https://skia-review.googlesource.com/c/skia/+/238196

Change-Id: Ifce43879685bf0d760a7e12dceb32f7a650be687
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247340
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
6 files changed