Add location notification and target sdk checks

Check target SDKs to disallow using setSecureSetting with LOCATION_MODE
and point clients to setLocationEnabled() instead. Show notifications to
users when location settings are changed by the admin.

Bug: 136219903
Test: manual - triggered setLocationEnabled and observed notification
Change-Id: I07c150e62230b06f76ec7bd5197a23e703ffb918
diff --git a/proto/src/system_messages.proto b/proto/src/system_messages.proto
index 54b4201..63dd99e 100644
--- a/proto/src/system_messages.proto
+++ b/proto/src/system_messages.proto
@@ -244,6 +244,10 @@
     // Package: android
     NOTE_SOFTAP_AUTO_DISABLED = 58;
 
+    // Notify the user that their admin has changed location settings.
+    // Package: android
+    NOTE_LOCATION_CHANGED = 59;
+
     // ADD_NEW_IDS_ABOVE_THIS_LINE
     // Legacy IDs with arbitrary values appear below
     // Legacy IDs existed as stable non-conflicting constants prior to the O release