Disable modifier window actions if global shortcuts are disabled

Summary:
Same is done on X11 (see Client::updateMouseGrab), so we should have this
on Wayland as well.

Also adding the pointer confinement restriction for modifier + wheel.

Test Plan: Run new and adjusted testcases with and without the change

Reviewers: #kwin, #plasma

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16025