Add physics picking backend using bevy_picking

[Jondolf]

Objective

Bevy 0.15 upstreams bevy_mod_picking as bevy_picking. Now that picking is first-party, we should add a collider picking backend, especially as bevy_mod_picking (which has an Avian backend) is on track for deprecation.

Solution

Add a PhysicsPickingPlugin! It is behind the bevy_picking default feature and must be added manually, but once it is enabled, picking is enabled for all colliders by default. Picking can be made opt-in using PhysicsPickingSettings::require_markers, in which case you must mark pickable entities with the PhysicsPickable component. The API and approach quite closely match the MeshPickingPlugin in Bevy 0.15.

The plugin is largely based on the Avian backend in bevy_mod_picking, with some tweaks to docs and naming. I also added a 2D version of the picking backend.

There is a new picking_3d example:

2024-11-11.02-56-18.mp4

(Note: The torus and conical frustum use trimesh colliders here, which is why the normals change a bit abruptly)

I have not added a 2D example (yet), but tested that it works:

2024-11-11.02-58-14.mp4