Replace isWeaklyValidatedHostname with guava

The guava implementation is more accurate than the basic NetworkUtils
implementation.
NetworkUtils is being moved to its own JAR and will not be available
from Settings.

Bug: 174436414
Test: m
      Wrote test for isWeaklyValidatedHostname, verified it passes with
      guava
Change-Id: I1d01f2beba36009e17f651652e2d7f57be5aa398

src/com/android/settings/network/PrivateDnsModeDialogPreference.java

@@ -28,7 +28,6 @@ import android.content.ContentResolver;
 import android.content.Context;
 import android.content.DialogInterface;
 import android.content.Intent;
-import android.net.NetworkUtils;
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.provider.Settings;
@@ -56,6 +55,8 @@ import com.android.settingslib.HelpUtils;
 import com.android.settingslib.RestrictedLockUtils;
 import com.android.settingslib.RestrictedLockUtilsInternal;
 
+import com.google.common.net.InternetDomainName;
+
 import java.util.HashMap;
 import java.util.Map;
 
@@ -278,7 +279,7 @@ public class PrivateDnsModeDialogPreference extends CustomDialogPreferenceCompat
         final Button saveButton = getSaveButton();
         if (saveButton != null) {
             saveButton.setEnabled(modeProvider
-                    ? NetworkUtils.isWeaklyValidatedHostname(mEditText.getText().toString())
+                    ? InternetDomainName.isValid(mEditText.getText().toString())
                     : true);
         }
     }