There are various picking optimizations we could do:

1. Remove use of HashMap / HashSet (or convert to LinkedHashSet)
    - Should just be able to reuse a single ArrayList, no object generation

2. Use PickRay everywhere
    - Make extremely lightweight, reuse PickRay to avoid object generation when picking

3. Need an "on read" hook for variables such as "hovered" (note that this needs compiler support).
    - Needed to have optimization where we pick less of the scene if nobody is listening
    - Not sure how this plays with event bubbling where we might not know if somebody needs the event