Make app pairs respond properly to disabled state

1) App pair member icons are now always redrawn when app pair icon is redrawn, allowing greyed out icons to be updated immediately when an app is disabled.
2) App pairs now check for disabled status when clicked. If one or both of the apps is disabled, app pair will not be launched, and the appropriate error message or affordance will be displayed.

Fixes: 323088270
Test: Manual
Flag: ACONFIG com.android.wm.shell.enable_app_pairs TEAMFOOD
Change-Id: I7f2af75db0d8579d5d04583c0d3ead32714768e4