PTZ permissions and InputDeviceInfo.getCapabilities() / devicechange event

[guidou]

It is possible for a camera to have the capture permission enabled, but PTZ disabled. In this case the PTZ capabilities should not be exposed. Once PTZ permission is given, getCapabilities() should be exposed.

Should this result in a devicechange event? I think it should because it's a change in the result of enumerateDevices(), but it is still part of the discussion of whether the event should be fired when there are changes visible to the UA or visible to the page in https://github.com/w3c/mediacapture-main/issues/966

cc @jan-ivar @youennf