Add tests for array assignment with narrowing conversions.

An assignment like `mediump int a[2] = myHighpIntArray;` should succeed
now that the previous CLs have landed; originally, this would have
caused a type-mismatch error.

Change-Id: I86ffe6a21d0c7fbe289eef95aebc2605412566aa
Bug: skia:12248
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437740
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
6 files changed