Reland "Introduce SkGlyphSourceBuffer"

This is a reland of 77c53087c1ea92bc6c7e436f60746da7605cad98

Original change's description:
> Introduce SkGlyphSourceBuffer
>
> SkGlyphSourceBuffer provides a system for taking rejected glyphs from
> one glyph drawing stage, and turns them into the source for the next stage.
> It is rarely used, so it tries to conserve memory.
>
> Change-Id: I5275ffa3e804fc494eb2f5803e0cf2d148a755f7
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248260
> Reviewed-by: Ben Wagner <bungeman@google.com>
> Commit-Queue: Herb Derby <herb@google.com>

Change-Id: Ib90508a21993b12c71ee86cbdeb51c4d4c2ec913
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249128
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
4 files changed