[effects/scale] Port to JavaScript

Summary:
Now, when the scripting effects API has all required ingredients to port
the Scale effect to JavaScript we finally can do it.

The main rationale for porting this effect to JavaScript is that
scripted effects API lets us focus more on what we want instead of
"how".

Visually, the ported version doesn't deviate from the C++ version.

Test Plan:
* Enable the Scale effect;
* Open/close a window.

Reviewers: #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: graesslin, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16478