Deprecate type aliases for WorldQuery::Fetch (#8843)

# Objective

`WorldQuery::Fetch` is a type used to optimize the implementation of
queries. These types are hidden and not intended to be outside of the
engine, so there is no need to provide type aliases to make it easier to
refer to them. If a user absolutely needs to refer to one of these
types, they can always just refer to the associated type directly.

## Solution

Deprecate these type aliases.

---

## Changelog

- Deprecated the type aliases `QueryFetch` and `ROQueryFetch`.

## Migration Guide

The type aliases `bevy_ecs::query::QueryFetch` and `ROQueryFetch` have
been deprecated. If you need to refer to a `WorldQuery` struct's fetch
type, refer to the associated type defined on `WorldQuery` directly:

```rust
// Before:
type MyFetch<'w> = QueryFetch<'w, MyQuery>;
type MyFetchReadOnly<'w> = ROQueryFetch<'w, MyQuery>;

// After:
type MyFetch<'w> = <MyQuery as WorldQuery>::Fetch;
type MyFetchReadOnly<'w> = <<MyQuery as WorldQuery>::ReadOnly as WorldQuery>::Fetch;
```

crates/bevy_ecs/src/query/fetch.rs

@@ -455,15 +455,18 @@ pub unsafe trait WorldQuery {
 /// This must only be implemented for read-only [`WorldQuery`]'s.
 pub unsafe trait ReadOnlyWorldQuery: WorldQuery<ReadOnly = Self> {}
 
-/// The `Fetch` of a [`WorldQuery`], which is used to store state for each archetype/table.
-pub type QueryFetch<'w, Q> = <Q as WorldQuery>::Fetch<'w>;
 /// The item type returned when a [`WorldQuery`] is iterated over
 pub type QueryItem<'w, Q> = <Q as WorldQuery>::Item<'w>;
-/// The read-only `Fetch` of a [`WorldQuery`], which is used to store state for each archetype/table.
-pub type ROQueryFetch<'w, Q> = QueryFetch<'w, <Q as WorldQuery>::ReadOnly>;
 /// The read-only variant of the item type returned when a [`WorldQuery`] is iterated over immutably
 pub type ROQueryItem<'w, Q> = QueryItem<'w, <Q as WorldQuery>::ReadOnly>;
 
+/// The `Fetch` of a [`WorldQuery`], which is used to store state for each archetype/table.
+#[deprecated = "use <Q as WorldQuery>::Fetch<'w> instead"]
+pub type QueryFetch<'w, Q> = <Q as WorldQuery>::Fetch<'w>;
+/// The read-only `Fetch` of a [`WorldQuery`], which is used to store state for each archetype/table.
+#[deprecated = "use <<Q as WorldQuery>::ReadOnly as WorldQuery>::Fetch<'w> instead"]
+pub type ROQueryFetch<'w, Q> = <<Q as WorldQuery>::ReadOnly as WorldQuery>::Fetch<'w>;
+
 /// SAFETY: no component or archetype access
 unsafe impl WorldQuery for Entity {
     type Fetch<'w> = ();