Migrate all AlertDialogs to AndroidX version

- Let test cases can be compatible with AndroidX AlertDialog.
- Theme of Transparent needs to support AndroidX AlertDialog.

Change-Id: I0789b66f52feef30ebab7fb824d0e39d5ae9cc96
Fixes: 111413092
Test: make RunSettingsRoboTests -j56

tests/robotests/src/com/android/settings/RestrictedSettingsFragmentTest.java

@@ -21,7 +21,6 @@ import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 
 import android.app.Activity;
-import android.app.AlertDialog;
 
 import com.android.settings.testutils.SettingsRobolectricTestRunner;
 
@@ -31,6 +30,8 @@ import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import androidx.appcompat.app.AlertDialog;
+
 @RunWith(SettingsRobolectricTestRunner.class)
 public class RestrictedSettingsFragmentTest {