Outline prepareFor(Mask/SDFT)Drawing

In preparation to do some engineering on these loops.

* Cleanup glyph bounds handling.

Change-Id: I430f5c2b95522c20df2f76d16029d85a35f95539
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/565653
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed