Add getSelfManagedPhoneAccounts() TelecomManager API.

This is consistent with the existing getCallCapablePhoneAccounts API
which is used to get the phone accounts capable of placing phone calls.

Test: CTS
Bug: 34159263
Merged-In: I1396c63a6882947cd66721528e53b6964a9091e0
Change-Id: I1396c63a6882947cd66721528e53b6964a9091e0