Use bulk API for bitmap glyph drawing

Using prepareForDrawing was overkill for this bitmap drawing, and it
can use the simpler bulk api. Additionally, simplify  prepareForDrawing
by removing the handle of the bitmap special case.

Change-Id: I09b2d71de28a1a50590265594aaf94593f001336
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/235597
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
6 files changed