selftests/hid: tablets: move the transitions to PenState

selftests/hid: tablets: move the transitions to PenState

Those transitions have nothing to do with `Pen`, so migrate them to
`PenState`.

The hidden agenda is to remove `Pen` and integrate it into `PenDigitizer`
so that we can tweak the events in each state to emulate firmware bugs.

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Jiri Kosina <jkosina@suse.com>
Link: https://lore.kernel.org/r/20231206-wip-selftests-v2-5-c0350c2f5986@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>