Allow subscribing to permission results via listener

I think it would be helpful if, in addition to overriding `onRequestPermissionsResult`, one could listen to permission results with a listener. That could be `LifecycleListener` or a dedicated interface.

Happy to submit a PR if this would be something you'd consider!

Start by locating the existing onRequestPermissionsResult callback and reviewing how LifecycleListener is defined and used. Compare those entry points with the proposed dedicated-interface option, then define the listener API and its permission-result delivery behavior. Done means the design is agreed and the resulting listener mechanism is covered by appropriate tests.

Written by the indexing model from the issue text.