Vulkan: Fix dirty state in XFB emulation on EndXFB. This regressed in "Vulkan: Preserve RPs on XFB changes when possible." The bug manifested as incorrect fire rendering in Manhattan. The fix is to ensure we dirty the correct buffer state when we call endXFB. Also adds a regression test. Bug: b/161744596 Bug: angleproject:4622 Change-Id: If16cc22b149526950f300e74c0cc82c0fefae5bc Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2368016 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Tobin Ehlis <tobine@google.com> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>