[XR] Allow choosing which hand/controller controls pointer selection while in session

[RaananW]

At the moment it is possible to define the preferred handedness or force pointer selection on both hands/controllers, but there is no way to change the controller in charge of pointer selection while in session.

[github-actions[bot]]

This issue has been automatically staled because it has been inactive for more than 14 days. Please update to "unstale".