Check collisions between two entities about avian

[musjj]

I went with the pattern from the example:

https://github.com/Jondolf/bevy_xpbd/blob/e4930ba220757b23774d7a0021a3deae238f0d02/crates/bevy_xpbd_2d/examples/one_way_platform_2d.rs#L257-L266

But yeah, a helper method would be nice.

[Jondolf]

Right now, you would need to iterate through collision events and manually find the collision with the correct entities. This isn't ideal of course, but I don't think there's a better way yet.

However, this will be much nicer in 0.3. On the main branch there is a new Collisions resource that allows you to do collisions.get(entity1, entity2), which should be what you want. This is somewhat WIP since there's still some issues, but they should be fixed by #112 once I have time to finish it.

[Jondolf]

I'll close this since Collisions is now properly working and usable on the main branch. It has get and get_mut which should work for your use case.