This makes LibraryLoader actually load the library and moves ownership
of GetInstanceProcAddr into it, which means we pass through the
loaders into their parents to grab stuff.
This was only half-implemented (e.g. OpenXR was still calling
GetModuleHandle), broke compilation with Vulkan due to mismatched ABI,
and wouldn't have worked anyways with winelib builds because we still
need access to wine's implementation of the Vulkan win32 winsys
integration. Perhaps this is still useful for dxvk-native but if so it
should be re-added under a DXVK_NATIVE flag.
