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().
This happened when the source texture was an EFB copy, therefore it had
not been populated prior to the draw command buffer being executed, and
the conversion was occurring in the init command list.
Stenzek