Vulkan: read pixel buffer alignment must be 4. BUG=angleproject:2867 Change-Id: Ie14848bb464eea7f84d0ce523dff2cddf7a185d4 Reviewed-on: https://chromium-review.googlesource.com/c/1260256 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Frank Henigman <fjhenigman@chromium.org>