[libkwineffects] Make AnimationEffect::AniMap protected

Summary:
We need AniMap only for test purposes so it would be better to make the
typedef protected (and mark as internal as well).

Test Plan: Compiles.

Reviewers: KWin, davidedmundson

Reviewed By: KWin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D17833