Allow picking subset of models in View3D

TLDR; please amend `PickResult pick(float x, float y)` to `PickResult pick(float x, float y, List<Model> included)` and optimize picking to only iterate over `included`.

I have millions of instanced `Model`s in my scene that are pickable. As expected without any sort of culling, picking runs slow at 10FPS (which is good enough).

However, every frame I would like to `pick` only a specific object to find its exact world coordinates that are in the 4 corners of the viewport.

I tried disabling picking for the instanced model right before picking this specific object (and turning it back on after picking), but for some reason this didn't work (bug?). Whether this behavior is a bug or not I'd love a 3rd optional param added to `pick` as an optimization.

Edit: Simply exposing `getRayFromViewportPos(point p)` would also let me do what I need to do picking