Consider subId when loading Wfc string resources

Consider subId when loading string resources in screen
WifiCallingSettingsForSub and Wi-Fi Calling slice.

This ensures that correct string resources is loaded in multi sim
scenario when operators are using customized strings.

Bug: 129893058
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WifiCallingPreferenceController
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WifiCallingSliceHelper
Change-Id: Ia5b763d4b59f7e738cb741b778bb859884a85198