UI/Layer filtering/priorities.

When you're inside a large model / overlapping one, like for example an ARR model, it can get hard to interact with UI objects.
It would be nice if it was possible to add a layer/priority system to the interaction-beams, so that it's always possible to interact with high-priority UI elements.

My thought here is to have the hand interaction beams pierce, instead of hit objects, and return the object with the highest UI priority.
So that if you're pointing at a model with priority 0, and behind it, a menu button with priority 5, events will get fired on the button, instead of getting 'hijacked' by the model.

Alternatively could do some gaze-filtering, where objects you're looking at are more important than ones you're not.
(Just y'know, filtering away models you're inside.)

No files, tests, or entry points are named. First locate the Unity HoloLens interaction-beam implementation and clarify whether priority-based piercing or gaze filtering is intended; the work is done when the selected UI behavior is implemented and its interaction cases are covered.

Written by the indexing model from the issue text.