vkd3d: Add a win32 version of vkd3d_get_program_name.
Taken from wined3d_get_app_name with some adjustments.
I'll use this for the default cache filename, but I think it makes sense on its own because we pass this information to Vulkan. Wine's d3d12 passes a struct vkd3d_application_info, but doesn't set the application name.