use SkStrikeSpec in remote and main strike cache

* Remove the SkDescriptor from SkScalerCache where it is never really
  used.
* Have SkStrike hold the descriptor
* Add a method to the SkStrikeSpec to create SkScalerContexts

Flow all the parameter changes through the code.

Change-Id: I11f2eec590b509eef0396b9288a6297fbe967dff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/468457
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
10 files changed