Create a global registry for system message IDs

Port all system UI notifications to use the registry.  Retain stable
integer IDs where they exist. Assign new stable IDs where resource IDs
were previously used.

Using "message" rather than "notification" since we may eventually
want to include dialogs and toasts.

Bug: 32584866
Bug: 30995038
Test: runtest systemui
Change-Id: Iec4d7cebbd88683e339ada29a279315222699942