This also moves the pipeline and descriptor set layouts used for texture
conversion (texel buffers) to ObjectCache, and shares a binding location
with the SSBO set.
There's not a lot of point in passing these around or storing them
(texture cache/state tracker mainly) as there will only ever be a single
instance of the class.
Also adds downcast helpers such as Vulkan::Renderer::GetInstance().
Léo Lam