Only load the inline script for animations if needed

[bfintal]

In the frontend, Stackable outputs this:

<script>requestAnimationFrame(() => document.body.classList.add( "stk--anim-init" ))</script>

Since this is only used for animations, we need to only add this when needed.

[andeng1106]

QA notes:

• If free build, should not load whether i have premium animations or not in the page
• If premium build, should only load when i have premium animations in the page