Summary:
While BuiltInEffects has effectData() function, many functions repeat
s_effectData.at(index(effect)), which is what effectData() is doing.

By using effectData(), we'll get rid of those repetitions and maybe make
easier transition to other underlying data structure that stores metadata
for builtin effects.

Test Plan: Compiles, all enabled builtin effects are loaded and working.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13587