Vulkan: Refactor imageless framebuffer creation Bug: angleproject:7551 Change-Id: I6789123d1b854a64ce405dd1e096b9c28a227b5f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5384139 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>