* Instead of only doing a very lightweight check to see if the API is available
up-front, we now share the API initialisation among all API tests far enough
to determine availability of extensions, features, etc. Then we can precisely
determine which tests are available and which aren't before running.
* We also pick the output pixel in the CBuffer_Zoo tests to ensure the API
agrees with our interpretation of the data.
* Follow-up commit will tidy D3D cbuffer code that needs it.
* Built entirely independently of the main renderdoc build (for now).
* Contains python scripts & framework for running tests on a renderdoc build,
which will be run nightly.