simple Debug impls for query iterators (#13476)

# Objective

The current query iterators cannot be used in positions with a `Debug`
bound.
F.e. when they are packaged in `Result` in the error position, `expect`
cannot be called on them.
Required for `QueryManyIter::entities_all_unique` in #13477.

## Solution

Add simple `Debug` impls that print the query iterator names.

## Changelog

`QueryIter`, `QueryManyIter`, `QueryCombinationIter`, and
`QuerySortedIter` now implement `Debug`.

crates/bevy_ecs/src/query/iter.rs

@@ -6,7 +6,14 @@ use crate::{
     storage::{Table, TableRow, Tables},
     world::unsafe_world_cell::UnsafeWorldCell,
 };
-use std::{borrow::Borrow, cmp::Ordering, iter::FusedIterator, mem::MaybeUninit, ops::Range};
+use std::{
+    borrow::Borrow,
+    cmp::Ordering,
+    fmt::{self, Debug, Formatter},
+    iter::FusedIterator,
+    mem::MaybeUninit,
+    ops::Range,
+};
 
 use super::{QueryData, QueryFilter, ReadOnlyQueryData};
 
@@ -857,6 +864,12 @@ impl<'w, 's, D: QueryData, F: QueryFilter> Iterator for QueryIter<'w, 's, D, F>
 // This is correct as [`QueryIter`] always returns `None` once exhausted.
 impl<'w, 's, D: QueryData, F: QueryFilter> FusedIterator for QueryIter<'w, 's, D, F> {}
 
+impl<'w, 's, D: QueryData, F: QueryFilter> Debug for QueryIter<'w, 's, D, F> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("QueryIter").finish()
+    }
+}
+
 /// An [`Iterator`] over sorted query results of a [`Query`](crate::system::Query).
 ///
 /// This struct is created by the [`QueryIter::sort`], [`QueryIter::sort_unstable`],
@@ -985,6 +998,14 @@ where
 {
 }
 
+impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator<Item = Entity>> Debug
+    for QuerySortedIter<'w, 's, D, F, I>
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("QuerySortedIter").finish()
+    }
+}
+
 /// An [`Iterator`] over the query items generated from an iterator of [`Entity`]s.
 ///
 /// Items are returned in the order of the provided iterator.
@@ -1131,6 +1152,15 @@ where
 {
 }
 
+impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> Debug for QueryManyIter<'w, 's, D, F, I>
+where
+    I::Item: Borrow<Entity>,
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("QueryManyIter").finish()
+    }
+}
+
 /// An iterator over `K`-sized combinations of query items without repetition.
 ///
 /// A combination is an arrangement of a collection of items where order does not matter.
@@ -1364,6 +1394,14 @@ impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter, const K: usize> FusedIterator
 {
 }
 
+impl<'w, 's, D: QueryData, F: QueryFilter, const K: usize> Debug
+    for QueryCombinationIter<'w, 's, D, F, K>
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("QueryCombinationIter").finish()
+    }
+}
+
 struct QueryIterationCursor<'w, 's, D: QueryData, F: QueryFilter> {
     storage_id_iter: std::slice::Iter<'s, StorageId>,
     table_entities: &'w [Entity],