Add DeviceRef::{location, location_number} and MTLDeviceLocation (#187)
Add DeviceRef::{location, location_number} and MTLDeviceLocation (#187)

* Add DeviceRef::{location, location_number}
Add MTLDeviceLocation

https://developer.apple.com/documentation/metal/mtldevice/3114006-locationnumber
https://developer.apple.com/documentation/metal/mtldevice/3114005-location
https://developer.apple.com/documentation/metal/mtldevicelocation

* Make `MTLDeviceLocation` a public type
gfx-rs/metal-rs,fkaa/metal-rs