Now that we have vk-unittests, it makes sense to prefix unittests by their API name.

Fixes a couple of TODOs

Change-Id: I57234d6b19c3dd4f130b211a0be4e604613b8cd8
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28399
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>