[canvaskit] Move matrix helpers to their own file and make optional.

Change-Id: I904a491134d5e3b19de8b7c34dcde30f1fd2487e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/362037
Reviewed-by: Nathaniel Nifong <nifong@google.com>
4 files changed