Split RapierContext

[Vrixyz]

• Fix https://github.com/dimforge/bevy_rapier/issues/502
• 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 https://github.com/dimforge/rapier.rs/pull/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: https://github.com/jakobhellermann/bevy_mod_debugdump/pull/50.