Explicitly disable pointer constraints on TabBox invocation

Summary:
Pointer constraints should become disabled when the TabBox is invoked. Since
the current client stays activated while TabBox is enabled and currently can
not be deactivated with the risk of regression as discussed in D13758, disable
all pointer constraining explicitly and enable it again when the TabBox is
closed.

Test Plan: Manually in Wayland session.

Reviewers: #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: kwin

Tags: #kwin

Maniphest Tasks: T8923

Differential Revision: https://phabricator.kde.org/D14142