Dispatch traits aren't composable

When processing queries on a compound shape, `QueryDispatcher` methods must be invoked recursively. This makes it infeasible for custom shapes that occur inside compound shapes to be handled. Ideally downstream code could provide `chain`able `QueryDispatcher` impls that only handle the shapes they introduce and otherwise return `Unsupported`, but in that case a compound shape would fall through to the default dispatcher, which would recurse internally and fail to handle custom shapes it encounters. Similar issues affect any user-defined composite shapes. This could be fixed by adding a `root_dispatcher: &dyn QueryDispatcher` argument to every trait method. The same issue also affects `PersistentQueryDispatcher`.

I can bang this out, but it's a bunch of boilerplate updates and given that this logic was not preserved from ncollide I want to be sure it's welcome before proceeding.