selftests/hid: tablets: add variants of states with buttons

Turns out that there are transitions that are unlikely to happen:
for example, having both the tip switch and a button being changed
at the same time (in the same report) would require either a very talented
and precise user or a very bad hardware with a very low sampling rate.

So instead of manually building the button test by hand and forgetting
about some cases, let's reuse the state machine and transitions we have.

This patch only adds the states and the valid transitions. The actual
tests will be replaced later.

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-v2-10-c0350c2f5986@kernel.org


Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>