Currently, the gamepad code uses a uint32_t as a handle and does some trickery
with it by trying to create a unique ID and adding an offset to it for VR code.
This can (and has) led to errors where the developer forgets to perform the
arithmetic and sends the wrong number to the wrong manager.
This change created a strongly-typed handle that remembers which service it
belongs to. This should eliminate such accidents.
Differential Revision: https://phabricator.services.mozilla.com/D96273
