Formalize DisconnectCause API

As part of telecom mainline, formalize the hidden DisconnectCause
constructor (used by Telephony) into a system API. Additionally, the
telephony related debug info getters also need to be formalized:
getTelephonyDisconnectCause, getTelephonyPreciseDisconnectCause,
getImsReasonInfo.

Bug: 322518612
Bug: 311773409
Test: atest DataObjectUnitTests
Change-Id: I5b723efb21291cbd5dc156aee501551080adb68b
1 file changed