This CL refines the feedback loop check to allow rendering to non-
sampled levels of currently bound textures. This is a technique
sometimes used to initialize a mip chain of a texture.

Also adds a regression test that fails on Vulkan.

Bug: angleproject:4500
Bug: angleproject:4690
Change-Id: I5fd370e36a2919c82170abcbd2b0897c075bdcc7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2367314
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>