This saves one pointer indirection every time a device function is called from a device client handle. I have similar changes for other wrappers.
One thing that could also be done, and which would then remove the need for the object_sizes metadata, is to move the unix struct definition within `struct VkDevice_T`, hiding the unixlib members from the PE side using `#ifdef WINE_UNIX_LIB` but I'm not sure it's much cleaner though, so maybe keeping the object sizes is better.