Add test of off-kilter matrix constructors.

This exposes a bug in the Metal code generator which will be resolved
in a followup CL.

Change-Id: If073835dbee474ea9a805eb92b42dc1fca2afbd0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/448378
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>