Add a test to expose location'ed varying link bug Bug: angleproject:4355 Change-Id: I2b914d3e6bf74ccf5d3f42d7bd010e44e45645ea Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2023921 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>