The DrawBuffers resetting logic didn't update the depth/stencil serial.
Fix this and add a regression test that would crash in this situation.
Note that the Manhattan benchmark could trigger this under some cases.

Bug: angleproject:4322
Bug: angleproject:4490
Change-Id: Ie4b24efeb5991ecaa85bf8f964f77476bd6f167d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2111333
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>