Use flag to control the hierarchy tree changes

This change includes these:
Regional preferences
-Temperature
-First day of week
-Numbering system
-Footer preference

Bug: 379962955
Flag: com.android.settings.flags.regional_preferences_api_enabled
Test: check hsv and atest FirstDayOfWeekControllerTest, NumberingSystemControllerTest, TemperatureUnitControllerTest
Change-Id: Icb628640c05f1f4bb974416c35dce16a14f84a6c