Better deletions

- Allow apps to delete notification groups (which cascade to delete all
channels therein)
- Allow apps to get their groups, so they know what they might want to
delete
- Don't throw if someone tries to delete something that already doesn't
exist.

Change-Id: I5f6e25497c5da1e57b52737586e86097332f88f9
Fixes: 36245468
Fixes: 36127382
Test: runtest systemui-notification, cts
diff --git a/core/java/android/app/INotificationManager.aidl b/core/java/android/app/INotificationManager.aidl
index 896f56c..5ea2480 100644
--- a/core/java/android/app/INotificationManager.aidl
+++ b/core/java/android/app/INotificationManager.aidl
@@ -67,6 +67,8 @@
     ParceledListSlice getNotificationChannelsForPackage(String pkg, int uid, boolean includeDeleted);
     int getNumNotificationChannelsForPackage(String pkg, int uid, boolean includeDeleted);
     int getDeletedChannelCount(String pkg, int uid);
+    void deleteNotificationChannelGroup(String pkg, String channelGroupId);
+    ParceledListSlice getNotificationChannelGroups(String pkg);
 
     // TODO: Remove this when callers have been migrated to the equivalent
     // INotificationListener method.