Fix bug where app pair title was not updating with language

This CL adds the ability for an app pair icon to update its title string when package changes are detected. It also reorganizes some code in the app pairs classes for readability.

Fixes: 316051810
Flag: ACONFIG com.android.wm.shell.enable_app_pairs TRUNKFOOD
Test: Manual
Change-Id: I833e4f9766b7da8c0a3a5fb4b9fc050d8897437e