Translator: Validate multi-declarations are separated Many transformations only look at the first variable in a TIntermDeclaration. This change validates that once the SeparateDeclarations transformation has been run, multi-declarations are not reintroduced. Bug: angleproject:2733 Change-Id: If5f96689cbdd28817c479dd7c495b91535f87199 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2815565 Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>