[Settings] Use background thread to get VoNr state.

- TelephonyManager#isVoNrEnabled may not send back the result in time,
   so use different thread and timer to prevent ANR.

Bug: 282876876
Test: atest passed
Change-Id: Ie6cc0f8a459f5ebed930e457dacb9b742df70fad

tests/unit/src/com/android/settings/network/telephony/NrAdvancedCallingPreferenceControllerTest.java

@@ -186,6 +186,7 @@ public class NrAdvancedCallingPreferenceControllerTest {
         doReturn(true).when(mTelephonyManager).isVoNrEnabled();
         mPreference.setChecked(false);
 
+        mController.init(SUB_ID);
         mController.updateState(mPreference);
 
         assertThat(mPreference.isChecked()).isTrue();