Add a header view to show the country in RegionZonePicker

Extra fixes in this CL
- Minor string update in time zone picker.
  Use date_time_search_region string in search bar,
  and date_time_set_timezone_title string for lower case "zone".
- Fixed b/76893139. Remove the unnecessary top padding in RecyclerView.
  Create a new layout file time_zone_items_list.xml without the padding.
- Add missing return statement when region ISO code
  is invalid in RegionZonePicker#getAllTimeZoneInfos

Bug: 76209571
Bug: 76893139
Test: m RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.datetime.timezone
Test: Verified that the strings are updated in the UI
Change-Id: I1fb3e2abf80da3cb53cfbc3363bbe46e40a6ac22

src/com/android/settings/datetime/timezone/BaseTimeZonePicker.java

@@ -44,7 +44,7 @@ import java.util.Locale;
  * The search matches the prefix of words in the search text.
  */
 public abstract class BaseTimeZonePicker extends InstrumentedFragment
-        implements SearchView.OnQueryTextListener{
+        implements SearchView.OnQueryTextListener {
 
     public static final String EXTRA_RESULT_REGION_ID =
             "com.android.settings.datetime.timezone.result_region_id";
@@ -84,7 +84,7 @@ public abstract class BaseTimeZonePicker extends InstrumentedFragment
     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
             Bundle savedInstanceState) {
-        final View view = inflater.inflate(R.layout.recycler_view, container, false);
+        final View view = inflater.inflate(R.layout.time_zone_items_list, container, false);
         mRecyclerView = view.findViewById(R.id.recycler_view);
         mRecyclerView.setLayoutManager(new LinearLayoutManager(getContext(),
                 LinearLayoutManager.VERTICAL, /* reverseLayout */ false));