Vulkan: Add multisample buffer age tests * Added variations of VerifyContent for multisample images. * getBufferAge() now sets age to 0 when the image is multisampled. Bug: angleproject:7149 Change-Id: I11f6fc92f383fba180f118b29c799072ed0eb51c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3563510 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>