Support confirmation of international calls while on WFC only.

Add new carrier config which enables a confirmation message when the user
dials an international number while on WFC only.

Add new @hide PhoneNumberUtils method which is used to determine if a
number dialed is an international number.

Test: Manual, unit.
Bug: 33272455
Change-Id: Ia7ffe10eee7d782ddc3355db616af0a48f19556e