Add a helper class for listening to subscription and airplane mode changes

For the new multi subscriptions UX, in several places we need to listen
for both subscription changes (eg a sim card was inserted or removed),
as well as airplane mode changing state. This combines those in one
helper class that can be reused.

Bug: 116349402
Test: make RunSettingsRoboTests
Change-Id: Ibcbb669ae291a917f89735dbda043742efaa58c9