libinput-debug-events prints keycodes as they come in. This makes it dangerous
to be run by users (especially in the background) because it will leak
sensitive information as it is typed. Obfuscate the base set of keycodes
by default, require a --show-keycodes switch to show it.

The few times we actually need the keycodes, we can run the switch in the
debugging tool.

This does not affect keys outside of the main block on the keyboard (F-keys,
multimedia keys).

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
(cherry picked from commit 8c1aa1de)