read/write m44

Inspired by https://skia-review.googlesource.com/c/skia/+/303271

Change-Id: I64816f8db1742d263c8f668a7b44a08f20d82f5e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/304065
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
7 files changed