Have connectivity self-register manager classes

As connectivity services are planned to move to a separate module, move
the manager classes registration from SystemServiceRegistry to
ConnectivityServicesRegistrar, using the registerContextAwareService
APIs.

This follows patterns and naming in WifiFrameworkInitializer.

Bug: 171540887
Test: device boots, connectivity working
Change-Id: I62ced1275750c73f209bac8ec3a3204b95695b83

framework/src/android/net/ConnectivityManager.java

@@ -4823,6 +4823,28 @@ public class ConnectivityManager {
         }
     }
 
+    /** @hide */
+    public TestNetworkManager startOrGetTestNetworkManager() {
+        final IBinder tnBinder;
+        try {
+            tnBinder = mService.startOrGetTestNetworkService();
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+
+        return new TestNetworkManager(ITestNetworkManager.Stub.asInterface(tnBinder));
+    }
+
+    /** @hide */
+    public VpnManager createVpnManager() {
+        return new VpnManager(mContext, mService);
+    }
+
+    /** @hide */
+    public ConnectivityDiagnosticsManager createDiagnosticsManager() {
+        return new ConnectivityDiagnosticsManager(mContext, mService);
+    }
+
     /**
      * Simulates a Data Stall for the specified Network.
      *