Input: properly queue synthetic events

We should not be passing synthetic events (such as autorepeat events)
out of order with the events coming from the hardware device, but rather
add them to pending events and flush them all at once.

This also fixes an issue with timestamps for key release events carrying
stale data from the previous autorepeat event.

Reviewed-by: Angela Czubak <acz@semihalf.com>
Link: https://lore.kernel.org/r/YszNfq4b6MkeoCJC@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>