Use connection token in CommandEntry

To prepare for the upcoming ANR refactor, use a connection token inside
CommandEntry instead of storing the entire input channel.

We don't actually need the entire input channel, because WM uses it to
look up windows using the token.

Bug: 171218828
Test: atest inputflinger_tests
Change-Id: Ia82f05685db2fcb7de3b8dc00c57e5d108baf902