Add `avian3d` support

[chompaa]

This PR adds support for avian3d via the avian feature. Here's a list of changes:

• Add a controller_avian module and minimal_avian example, feature gated behind the avian feature.
• Move the controller to controller_rapier and minimal example to minimal_rapier feature gating them behind the rapier feature.
• Add a controller module that reexports both controller modules, so you can still import with use bevy_fps_controller::controller::*

I think there is a bug with overhang_component in controller_avian, since edge fall prevention doesn't seem to be working 100% of the time -- I couldn't crack this unfortunately. My (minimal) testing has shown identical behavior otherwise.

I understand that this is a large diff, so if you'd like a different approach I'd be happy to comply.

[qhdwight]

Woah nice! I will take a look, thanks

[qhdwight]

Hey - mind rebasing?

[chompaa]

Hey - mind rebasing?

Hey! I'll try to get around to this in the next few days :)

[qhdwight]

Thanks. I rebased and fixed up the compilation in the avian branch for my own testing.

It seems like it is a little bit choppy? Can you see this on your end?

[qhdwight]

Also - I think we should seek to minimize copy and paste by sharing common functions among both features that are the same.

i.e. fps_controller_look fps_controller_input FpsController, etc.

That way when we update, the pain is minimized.

[qhdwight]

I think there is a bug with overhang_component in controller_avian, since edge fall prevention doesn't seem to be working 100% of the time -- I couldn't crack this unfortunately. My (minimal) testing has shown identical behavior otherwise.

I am also seeing this too. Seems like this line is to blame:

// Make sure that this is actually a ledge, e.g. there is no ground in front of us
let cast = spatial_query.cast_ray(
  future_position + Vec3::Y * 0.125,
  Dir3::new_unchecked(-Vec3::Y),
  0.375,
  false,
  &filter,
);

Sometimes I can get stuck on the ledge when crouching and can't move at all. I would expect the above to return Some, but it returns None instead. The ray origin and direction looked good, so I am confused.

[qhdwight]

Closing in favor of #53

Will come back to these other issues