decouple TelecomManager#getSelfManagedPhoneAccounts (1/3)

Recently TelecomManager#getSelfManagedPhoneAccounts was updated
to allow callingPackages to get their PA's.  However, API council
noted there was ambiguity with what was returned from the method.
Thus the method has been decoupled into 2 methods.

bug: 216640181
Test: CTS
Change-Id: I3931fc999937aaafa34d08ca9eb21af72ab960b1