Support (non-editable) display of DND with a filter != PRIORITY

Whenever setInterruptionFilter() is called with NONE or ALARMS, the Do Not Disturb mode now shows the current policy (nothing allowed or alarms/media allowed), instead of the normal PRIORITY policy. This policy is read-only in the UI since it cannot be customized.

This should be, or at least become, pretty rare (with small exceptions, apps targeting V that call setInterruptionFilter() will use an implicit mode instead of changing the global zen mode, plus using these filters is quite nonstandard in itself).

Fixes: 361586248
Test: atest & manual (toggling DND via cmd shell)
Flag: android.app.modes_ui
Change-Id: If2439480235d30aa310ad8925341183b9761784c