This should enable some cases of limited support for feedback loops
with depth/stencil buffers. For example with Manhattan and the Vulkan
back-end.

Increases the number of RenderPasses in Manhattan slightly. This will
regress performance slightly until we can work out a better solution
that is also conformant with the spec.

Bug: angleproject:4517
Change-Id: I2758e6b4c2a930474c09cdc0950f3b6c34541089
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2106670
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>