zink: codegen improvements
We've got code generation for screen stuff now, but we're missing something sort of important: auto-detection of features required by specific VK versions.
As an example, VK_KHR_maintenance2 was promoted to core for VK 1.1, which means that if we have a 1.1+ instance, we should be setting have_KHR_maintenence2
true unconditionally.