AttributionSource: Deprecate setNext, add new setNextAttributionSource

setNext accepts a null argument, which is problematic from a security
standpoint. The utility of this is pretty much nonexistent and can lead
to check-for-null vulnerabilities. This patch deprecates setNext and
adds a new setNextAttributionSource which does the same thing, but does
not accept null arguments.

Bug: 271291107
Test: CTS test
Change-Id: If512274a3a477a71982178323cd4fd63ad1609e3