[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

core/java/android/net/NetworkStateSnapshot.java

@@ -24,6 +24,8 @@ import android.annotation.SystemApi;
 import android.os.Parcel;
 import android.os.Parcelable;
 
+import com.android.net.module.util.NetworkIdentityUtils;
+
 import java.util.Objects;
 
 /**
@@ -124,4 +126,15 @@ public final class NetworkStateSnapshot implements Parcelable {
     public int hashCode() {
         return Objects.hash(network, networkCapabilities, linkProperties, subscriberId, legacyType);
     }
+
+    @Override
+    public String toString() {
+        return "NetworkStateSnapshot{"
+                + "network=" + network
+                + ", networkCapabilities=" + networkCapabilities
+                + ", linkProperties=" + linkProperties
+                + ", subscriberId='" + NetworkIdentityUtils.scrubSubscriberId(subscriberId) + '\''
+                + ", legacyType=" + legacyType
+                + '}';
+    }
 }