Implement InputConnection task cancellation

This CL introduces the task cancellation mechanism into
RemoteInputConnection and RemoteInputConnectionImpl.

The code idea is to ignore InputConnection tasks if the session IDs do
not match.  By incrementing the session ID upon every "interruption",
we can effectively cancel any pending events issued before the
"interruption" happened.

Note that even with this CL RemoteInputConnection and
RemoteInputConnectionImpl still uses "0" as the session ID.
Hence there should be no user observable behavior change yet.

Fix: 203086369
Test: presubmit
Change-Id: I383c3958d2ac1a8d217706509fa12a92b381bbb3