Rename viewMatrix to drawMatrix, initialMatrix, or currentMatrix

The viewMatrix has three different uses.
* drawMatrix is the matrix passed in by the drawTextBlob.
* initialMatrix is drawMatrix this a blob was created with.
* currentMatrix describes what stored in the SubRun.

Change-Id: Idd547f079950385485a279d22728f03145d5a77f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/259834
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed