Introduce SkGlyphPositionRoundingSpec.

SkGlyphPositionRoundingSpec encapsulates the information needed for rounding
positions correctly. This allows test to avoid using an SkStrike in future
unit tests.

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

Change-Id: I18dd6fe394df0fcbda492cefe2484c9bf9bb40d1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247338
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
7 files changed