[tests] Add pointer constraints test

Summary:
Provides a testing application for pointer locking and pointer confining in
a Wayland session.

The application can be started with QT_QPA_PLATFORM variable set to wayland
or xcb to test constraining in native mode as well as through Xwayland.

Several modes and properties can be selected to test various forms of locking
and confining.

Reviewers: KWin, davidedmundson

Reviewed By: KWin, davidedmundson

Subscribers: davidedmundson, zzag, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D13439