Need standard way to handle interface moves.

[jpmedley]

PR #3154 replaces "alternative_name": "navigator.getDisplayMedia" with a note stating the same because as someone put it, 'alternative_name is meant to cover a change in name, not a move from one interface to another.'

I've seen moves happen often enough that there should be a JSON way of describing them. This seems to happen most frequently in the case of a method or property moving to an interfaces parent class.

[Elchi3]

Duplicate of #3463