Implement IntoIterator for Populated and borrows (#19441)

# Objective

`Populated`, a loose wrapper around `Query`, does not implement
`IntoIterator`, requiring either a deref or `into_inner()` call to
access the `Query` and iterate over that.

## Solution

This pr implements `IntoIterator` for `Populated`, `&Populated`, and
`&mut Populated`, each of which forwards the call to the inner `Query`.
This allows the `Populated` to be used directly for any API that takes
an `impl IntoIterator`.

## Testing

`cargo test` was run on the `bevy_ecs` crate
```
test result: ok. 390 passed; 0 failed; 2 ignored; 0 measured; 0 filtered out; finished in 46.38s
```

Author: zacryol

crates/bevy_ecs/src/system/query.rs

@@ -2627,6 +2627,36 @@ impl<'w, 's, D: QueryData, F: QueryFilter> Populated<'w, 's, D, F> {
     }
 }
 
+impl<'w, 's, D: QueryData, F: QueryFilter> IntoIterator for Populated<'w, 's, D, F> {
+    type Item = <Query<'w, 's, D, F> as IntoIterator>::Item;
+
+    type IntoIter = <Query<'w, 's, D, F> as IntoIterator>::IntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
+impl<'a, 'w, 's, D: QueryData, F: QueryFilter> IntoIterator for &'a Populated<'w, 's, D, F> {
+    type Item = <&'a Query<'w, 's, D, F> as IntoIterator>::Item;
+
+    type IntoIter = <&'a Query<'w, 's, D, F> as IntoIterator>::IntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.deref().into_iter()
+    }
+}
+
+impl<'a, 'w, 's, D: QueryData, F: QueryFilter> IntoIterator for &'a mut Populated<'w, 's, D, F> {
+    type Item = <&'a mut Query<'w, 's, D, F> as IntoIterator>::Item;
+
+    type IntoIter = <&'a mut Query<'w, 's, D, F> as IntoIterator>::IntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.deref_mut().into_iter()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{prelude::*, query::QueryEntityError};