Fallback 1: if display names are the same, use the last 4 digits of a
phone number
Fallback 2: if the phone number cannot be displayed or the last 4 digits
are identical, fallback to use the subscription id
This function depends on DeviceInfoUtils for the phone number
formatting. Because DeviceInfoUtils is within SettingsLib, this function
(at least for now) is located within the Settings codebase itself.
go/unique-sub-display-names
Bug: 148303118
Bug: 150370656
Test: atest -c SubscriptionUtilTest
Change-Id: Id3e26254d4b193c13506df52fb59e97643df7a32
2fb7e1bbc4