Implement the methods of RapierContext on RapierContextItem instead

[`RapierContext`](https://docs.rs/bevy_rapier3d/0.31.0/bevy_rapier3d/plugin/context/systemparams/struct.RapierContext.html) has various methods that can be used to query the simulated world. Problem is - you never actually get a value (or even reference) of the type `RapierContext`. Bevy queries don't return the item itself - instead they return its [`QueryData::Item`](https://docs.rs/bevy_rapier3d/0.31.0/bevy_rapier3d/plugin/context/systemparams/struct.RapierContext.html#associatedtype.Item). In our case - it's [`RapierContextItem`](https://docs.rs/bevy_rapier3d/0.31.0/bevy_rapier3d/plugin/context/systemparams/struct.RapierContextItem.html), which is generated automatically by the `#[derive(query::QueryData)]` and does not have any of these methods, making them unusable.

If these methods were implemented on `RapierContextItem` instead of `RapierContext` (which should be doable even if `RapierContextItem` itself is generated by a macro) then `Query<&RapierContext>` would be usable (currently it isn't)