Perform basic pass-fail checks in MatricesNonsquare.

Previously, it was structured like Matrices.sksl and had no verification
of its results. Now it double-checks that its outputs match our
expectations. The test is still quite simple for now, however.

Change-Id: Iaa45fe58beb497a63801833f8ba5a493a61139d9
Bug: skia:11985, skia:12003
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408646
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
6 files changed