This CL adds unit tests for the array accessor expression class.
Change-Id: I97a7b366a2303b071040164cbcda404fe0592d90
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16281
Reviewed-by: David Neto <dneto@google.com>
Reviewed-by: Dan Sinclair <dsinclair@google.com>