Fix set during render warnings <a2-repeat-loop>

[mikemitchel]

PM2 logs on DAT showing this warning:
ap[] is being set in render <a2j-repeat-loop>. This can cause infinite loops and performance issues. Use getters and listeners to derive properties instead. https://canjs.com/doc/guides/logic.html#Derivedproperties

Should likely happen in A2J author as well as this is a shared component. Possibly happening in other components as well.