Stresses the RenderPass buffer tracking in the Vulkan back-end.

Bug: angleproject:4950
Change-Id: I33d38d8703d0e333d0092195d34228d90f1af52a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2358522Reviewed-by: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>