Added default data subscription changed callback

Replaced the broadcast intent with the much efficient internal
callback.

Test: Basic telephony functionality tests
Test: atest PhoneSwitcherTest SubscriptionManagerServiceTest
Flag: com.android.internal.telephony.flags.dds_callback
Bug: 353723350
Change-Id: Ib066d0bfe321bd6cf41c9c9b8a6c1d40316a0ed9