standardize system notification IDs

All the trivial cases, plus some fixes to try to
mitigate collisions with the complex ones.

Complex services to follow in another CL,

Bug: 32584866
Test: make framework services
Change-Id: Ie9663600171d8ede11676e9d66f009dbb06def03
diff --git a/services/core/java/com/android/server/connectivity/Vpn.java b/services/core/java/com/android/server/connectivity/Vpn.java
index 9fc2fc7..2eb5557 100644
--- a/services/core/java/com/android/server/connectivity/Vpn.java
+++ b/services/core/java/com/android/server/connectivity/Vpn.java
@@ -81,6 +81,7 @@
 import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.messages.nano.SystemMessageProto.SystemMessage;
 import com.android.internal.net.LegacyVpnInfo;
 import com.android.internal.net.VpnConfig;
 import com.android.internal.net.VpnInfo;
@@ -1304,7 +1305,8 @@
                             .setVisibility(Notification.VISIBILITY_PUBLIC)
                             .setOngoing(true)
                             .setColor(mContext.getColor(R.color.system_notification_accent_color));
-            notificationManager.notifyAsUser(TAG, 0, builder.build(), user);
+            notificationManager.notifyAsUser(TAG, SystemMessage.NOTE_VPN_DISCONNECTED,
+                    builder.build(), user);
         } finally {
             Binder.restoreCallingIdentity(token);
         }