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/+/2368016Reviewed-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>