zink: generate code for instance creation
This was something suggested by @zmike earlier in !7383 (merged).
Note that the MoltenVK stuff are all hardcoded into the template, as the name "MoltenVK" breaks all sorts of assumptions the generator makes because it expects the standard "VK_VENDOR_extension" naming scheme. Also the file names are all subject to bikeshedding. ;)
Right now, zink_instances
is used, and zink_device_instances
is proposed.
The first four patches are from !7756 (merged).