[graphite] Add Geometry creation for text.

Adds SubRunData class to wrap all of the necessary data to be passed
to the text Renderers.

Bug: skia:13118
Change-Id: I0bc9988400817951abc0876dc56197b89ce0bcfd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/553586
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
10 files changed