[Provider Model] Show "!" icon when Wi-Fi is not validated (panel)

- Screenshot:
  https://screenshot.googleplex.com/BLNcfXiJFnuoT9N

Bug: 185454486
Bug: 185637977
Bug: 186543071
Test: manual test
atest -c ProviderModelSliceTest
make RunSettingsRoboTests ROBOTEST_FILTER=WifiSliceTest

Change-Id: Idff6bb8b394db5553cf399d2020aa28d9dedfc74

src/com/android/settings/wifi/WifiUtils.java

@@ -35,7 +35,8 @@ import com.android.wifitrackerlib.WifiEntry;
 
 import java.nio.charset.StandardCharsets;
 
-public class WifiUtils {
+/** A utility class for Wi-Fi functions. */
+public class WifiUtils extends com.android.settingslib.wifi.WifiUtils {
 
     private static final int SSID_ASCII_MIN_LENGTH = 1;
     private static final int SSID_ASCII_MAX_LENGTH = 32;