[effects/dimscreen] Port to JavaScript

Summary:
The ported effect looks quite similar to the C++ version except one
thing: it works correctly when user activates/deactivates a full
screen effect, for example the Desktop Cube effect.

Other than that, there are no behavioral or visual differences.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16452