Fixed accessibility issues in VPN Settings

- Show "(required)" and errors in required fields to alert users

- Show "(optional)" below each optional field

Bug: 386025633
Flag: EXEMPT bugfix
Test: Manual testing
  atest WifiConfigController2Test
Change-Id: Iefbd68e6658af7b073db219b3e04e94805092759

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

@@ -28,7 +28,7 @@ import android.widget.TextView;
 import androidx.appcompat.app.AlertDialog;
 
 import com.android.settings.R;
-import com.android.settings.wifi.utils.SsidInputGroup;
+import com.android.settings.wifi.utils.TextInputGroup;
 import com.android.settings.wifi.utils.WifiDialogHelper;
 import com.android.settingslib.RestrictedLockUtils;
 import com.android.settingslib.RestrictedLockUtilsInternal;
@@ -120,7 +120,8 @@ public class WifiDialog extends AlertDialog implements WifiConfigUiBase,
         }
 
         mDialogHelper = new WifiDialogHelper(this,
-                new SsidInputGroup(getContext(), mView, R.id.ssid_layout, R.id.ssid));
+                new TextInputGroup(mView, R.id.ssid_layout, R.id.ssid,
+                        R.string.vpn_field_required));
     }
 
     @SuppressWarnings("MissingSuperCall") // TODO: Fix me