Expose 4x4 matrices on canvas in a way similar to SimpleMatrix, add example.

Bug: skia:9866
Change-Id: I718455743e482e4f60a462027b629dc19b1dbad3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270201
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
8 files changed