Move bmp/mask/sdf functionality from GrTextUtils to GrAtlasTextContext

Change-Id: I3924f2f9fd2860749f0404030d0be502a8153faa
Reviewed-on: https://skia-review.googlesource.com/68211
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
4 files changed