Show dialog when user changes the region

1. show dialog for changing the region of system language
2. Show dialog for changing the region of non-system language

Bug: 390347399
Test: manual verification
Test: atest SettingsRoboTests:com.android.settings.localepicker.SystemLocaleSuggestedListPreferenceControllerTest
Test: atest SettingsRoboTests:com.android.settings.localepicker.SystemLocaleAllListPreferenceControllerTest
Test: atest SettingsUnitTests:com.android.settings.localepicker.SystemLocaleSuggestedListPreferenceControllerTest
Test: atest SettingsUnitTests:com.android.settings.localepicker.SystemLocaleAllListPreferenceControllerTest
Flag: com.android.settings.flags.regional_preferences_api_enabled
Change-Id: I5717f472143fc69efdbeaeaaca9c9ed9db56b397