Exempt emergency notifications from attentuation

 Notifications from packages with RECEIVE_EMERGENCY_BROADCAST permission
 are exempted from audio/vibration attentuation.

Flag: com.android.server.notification.polite_notifications_attn_update
Test: atest com.android.server.notification.NotificationAttentionHelperTest#testBeepVolume_politeNotif_exemptEmergency
      atest com.android.server.notification.NotificationAttentionHelperTest#testBeepVolume_politeNotif_Avalanche_exemptEmergency
Bug: 339152628
Change-Id: Ie00d6f98f182796c9207029082d8246ee23c91d3