Moved SmscIdentity to SMSManager also made it SystemApi

Bug: 260577776
Test: atest cts/tests/tests/telephony/current/src/android/telephony/cts/SmsManagerTest.java#testGetSmscIdentity
Change-Id: I1a6e206f0c7970a93e0def7012b4fe9ea8d6dcb8
4 files changed