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/RegionSearchPicker.java

@@ -48,7 +48,7 @@ public class RegionSearchPicker extends BaseTimeZonePicker {
     private TimeZoneData mTimeZoneData;
 
     public RegionSearchPicker() {
-        super(R.string.date_time_select_region, R.string.search_settings, true, true);
+        super(R.string.date_time_select_region, R.string.date_time_search_region, true, true);
     }
 
     @Override
@@ -60,7 +60,8 @@ public class RegionSearchPicker extends BaseTimeZonePicker {
     protected BaseTimeZoneAdapter createAdapter(TimeZoneData timeZoneData) {
         mTimeZoneData = timeZoneData;
         mAdapter = new BaseTimeZoneAdapter<>(createAdapterItem(timeZoneData.getRegionIds()),
-                this::onListItemClick, getLocale(), false);
+                this::onListItemClick, getLocale(), false /* showItemSummary */,
+                    null /* headerText */);
         return mAdapter;
     }