[FUI22] Support getAllNetworkStateSnapshot

Currently, ConnectivityService has getAllNetworkState but it is
not ideal to expose as system API since the plan is to get rid
of NetworkState. Thus, create a new one that returns
NetworkStateSnapshot to fulfill the needs.

Note the original getAllNetworkState cannot be deleted now since
it has @UnsupportedAppUsage annotation.

Test: atest FrameworksNetTests
Bug: 174123988
Change-Id: Icddd434552b0e9ecbc8299e7242ec88cf3145aca

framework/src/android/net/ConnectivityManager.java

@@ -1258,6 +1258,25 @@ public class ConnectivityManager {
         }
     }
 
+    /**
+     * Return a list of {@link NetworkStateSnapshot}s, one for each network that is currently
+     * connected.
+     * @hide
+     */
+    @SystemApi(client = MODULE_LIBRARIES)
+    @RequiresPermission(anyOf = {
+            NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK,
+            android.Manifest.permission.NETWORK_STACK,
+            android.Manifest.permission.NETWORK_SETTINGS})
+    @NonNull
+    public List<NetworkStateSnapshot> getAllNetworkStateSnapshot() {
+        try {
+            return mService.getAllNetworkStateSnapshot();
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
+
     /**
      * Returns the {@link Network} object currently serving a given type, or
      * null if the given type is not connected.