Looking back at the current INPUT_LISTENER_CB_DEFINE api naming, it
feels like it's a bit overloaded. Rename it to a simpler
INPUT_CALLBACK_DEFINE.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
Add some initial tests for the input subsystem, covering all the APIs in
both synchronous and thread mode.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>