Force single glyph calls through bulk interface

Enance SkBulkGlyphMetrics, SkBulkGlyphMetricsAndPaths, and SkBulkGlyphMetricsAndImages
with single glyph calls. In addtion, add calls needed to have the rest of the system
work with these interfaces.

As a resulte move the glyph, prepareImage, and preparePath calls to private.

Change-Id: I8d383b649390e45f621dcb9d62fb8367a55cee02
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254056
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
12 files changed