Use the constant evaluated value instead of manually traversing
variables to find the literal value. This is a small step towards
supporting 'const' values for array sizes.
Also make our OOB-byte related error diagnostics consistent.
Bug: tint:1580
Change-Id: Idf9eb22cdbf69d750218c554e9f826c30458c6b9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94600
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>