Summary:
There were several reasons to rewrite the Minimize Animation effect in
JavaScript: to simplify code and to get rid of full repaints. One could
say that nothing prevents us from calculating the dirty region in
postPaintScreen or postPaintWindow and it is correct, but with the
scripting effects API the dirty region will be calculated for us, so we
can focus more on "what we want" instead of "how".

Visually, the "old" effect and the rewritten one look quite the same.
Except one tiny bit: if a window doesn't have an icon in the task manager,
it won't be animated. The reason for that is the purpose of this effect is
to show where the window will be after it's minimized, if the window
doesn't have icon in the task manager, one can't click at the center of
the screen to unminimize the window.

There is one significant change, the name of the effect was changed to
"Squash". If we put this effect and the Magic lamp effect under "Window
Minimize Animation" category (or if we add some "heading" label), then
the old name and the name of the category would "conflict". The new name
was suggested by Nate Graham and it very closely describes what the
effect does. "Scale" doesn't fit this effect because while a window is
being animated, its aspect ratio is not preserved.

Reviewers: #kwin, #plasma, davidedmundson

Reviewed By: #kwin, #plasma, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16372