The new public API returns and notifies changes to the currently active
transport medium for the application. And there's a new private API to
report it, with backends to follow.
Task-number: QTBUG-91023
Change-Id: I527985f9dabcd7bc4a32f36597e21bc4ab664c4e
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>