Support Apple CarPlay (voice interface)

[gnprice]

We heard a feature request to add support for Apple CarPlay. The purpose of this from a user perspective is

to have the ability to hear the messages read out loud and respond to them with voice commands.

The relevant upstream docs are here:
https://developer.apple.com/carplay/
https://developer.apple.com/design/human-interface-guidelines/carplay/overview/messaging-and-voip-apps/

I haven't yet looked into what would be involved in this from an implementation perspective.

See also #5128 for the corresponding Android feature request.