Translator: Validate consistent variable references Some transformations change variable declarations. This validation ensures that all references to said variables are appropriately replaced as well. Bug: angleproject:2733 Change-Id: I6c2873968eeed4cba66e70069f84eb69a1f77074 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2818140 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>