Input: make events() method return number of events processed

Input: make events() method return number of events processed

In preparation to consolidating filtering and event processing in the
input core change events() method to return number of events processed
by it.

Reviewed-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240703213756.3375978-4-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>