picking backend

[Vrixyz]

• optional marker consideration
• feature gated
• optional check for entity (render) layers
  • further optimizations could check for rapier layers
• optional inherited visibility check
  • optional check for VisibleInView ; rapier currently does not support it so I'm considering that out of scope
    • we could support it for existing VisibleInView ; but it would be relying on other crates (mesh/sprites aabb ?), so the current "barebone" example couldn't profit from it, and come up as a surprise for users.
• consider optimisations with PickingBehaviour

[Vrixyz]

now dimforge#613