Summary:
This fixes a regression introduced with a1afeded.
The connections were setup every the windowShown signal got emitted.
This caused effects to get multiple singals and start multiple animations
which then do not get cancelled correctly.

The incorrect behavior was most visible in the translucency effect which
did not cancel the move animation and the window stayed translucent.

BUG: 366081

Test Plan:
New test case which simulates the behavior of the translucency
effect.

Reviewers: #kwin, #plasma, sebas

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D2346