servo: Merge #17488 - Replace iterator struct with anonymous return iterator type (from frewsxcv:frewsxcv-return-node-list); r=jdm

```
hi servo. it's been
some time. here's a pull request.
i hope you like it.
```

Source-Repo: https://github.com/servo/servo
Source-Revision: bc5e8f89fff9bf1922638b3eb2f4c75148dcad1e

Author: frewsxcv

servo/components/script/dom/nodelist.rs

@@ -103,11 +103,9 @@ impl NodeList {
         }
     }
 
-    pub fn iter(&self) -> NodeListIterator {
-        NodeListIterator {
-            nodes: self,
-            offset: 0,
-        }
+    pub fn iter<'a>(&'a self) -> impl Iterator<Item=Root<Node>> + 'a {
+        let len = self.Length();
+        (0..len).flat_map(move |i| self.Item(i))
     }
 }
 
@@ -289,18 +287,3 @@ impl ChildrenList {
         self.last_index.set(0u32);
     }
 }
-
-pub struct NodeListIterator<'a> {
-    nodes: &'a NodeList,
-    offset: u32,
-}
-
-impl<'a> Iterator for NodeListIterator<'a> {
-    type Item = Root<Node>;
-
-    fn next(&mut self) -> Option<Root<Node>> {
-        let result = self.nodes.Item(self.offset);
-        self.offset = self.offset + 1;
-        result
-    }
-}