Introduce bulk strike api for glyph metrics for one draw case

The strike system can determine which glyphs are important,
and will only put the important glyphs into the result.

This is only used in the draw mask case now. I will expand it to
the other cases. I'm leaving the existing abi inteact until all
cases are converted.

Change-Id: I8c5e785ccd4341adfb09888532bf7b690ffb91d4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/200048
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>