Switch to bulk api for GPU mask (BMP) drawing.

* Switch from processing a single glyph at a time to processing
  all with the same drawing type.

Change-Id: Id67b713f2f5a486be63fdcfee5012e73f3592cdf
Reviewed-on: https://skia-review.googlesource.com/c/182000
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
2 files changed