encapsulate GrSDFTOptions better

The logic for picking what type of sub run to create is spread
over several locations. Gather that altogether in drawingType().

Have GrSDFT close over all the data needed to calculate the
drawing type. This reduces plumbing to the processGlyphRun
routine.

The next CL should rename GrSDFTOptions to GrSDFTControl.

Change-Id: I99e74c11af6d3b3d9919e54fe1e7286fcfbf1bfb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/378036
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
13 files changed