Pointer to GrStrikeCache on GrTextBlob

This will allow all the glyph drawing closures to live on the
GrTextBlob.

Other cleanup
* Rename glyphCache things to grStrikeCache.

Change-Id: I03e0353a1434230086a08184221272f1e5751ae6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/197244
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>