Properly handle release of a touch resource

Summary:
On client side use wl_touch_release to get into the proper destroy
handler on server side. There the shared destroy implementation is
used.

The test case is extended to verify the condition and ensure that
our code doesn't crash in case SeatInterface calls into the already
unbound TouchInterface.

Reviewers: Plasma on Wayland

Subscribers: plasma-devel

Tags: Plasma on Wayland

Differential Revision: https://phabricator.kde.org/D2035