WIP: vkr: use generated proc tables
As we start adding extensions, it becomes obvious we want to generate more code. This is the first step to generate the code to initialize driver dispatch tables using vkGetDeviceProcAddr / vkInstanceDeviceProcAddr.
This is untested and is wip. @rakko has also started https://gitlab.freedesktop.org/rakko/virglrenderer/-/commits/update-venus-protocol. We might want to land that first which also gives us ideas what to generate.