Split RapierContext

[ThierryBerger]

• Improves Split up RapierContext #502
• Improves Use required components #605
• Required components are used for RapierContextSimulation
• splits out the following components from RapierContext:
  • colliders
  • joints
  • query pipeline
  • rigidbody set
• add example for accessing individual components
• RapierContext is now a QueryData aggregating all previously available information from that.
• prepared an updated userguide for rapier.rs at Bevy rapier 0.28 split context rapier.rs#120

Opportunities for parallelized execution seem limited, but exist, this also enables better separation of systems, with more typed information leading to a clearer intent.

I'm not 100% convinced it's a net positive in terms of maintainability, bevy_mod_debugdump is currently harder to read due to this bug: jakobhellermann/bevy_mod_debugdump#50.

[sebcrozet]

🎉

[ThierryBerger]

We could avoid this indirection to single() if we implemented all methods of RapierContext on its systemParam ; but:

• it would require making the query each time we call a method
  • Probably not so much of an issue if queries are cached
• it would require to add another 400 lines of code, I already fear for the maintenance of current layer of indirection, I'd like to keep it at the minimum.
  • a declarative macro to generate those ended up a bit too complex, and not much lines saved
  • maybe a procedural or a template step could be interesting.

[ThierryBerger]

Most of added lines come from this file, which holds a shortcut to functions users are accustomed to. Rather than looking up which component they have to rely on, they have a RapierContext-like API, and can look into it to see what queries it resolves to if they want.