docutils: Add missing dunders to nodes.Element (#7377)

stubs/docutils/docutils/nodes.pyi

@@ -1,4 +1,6 @@
-from typing import Any
+from _typeshed import Self
+from collections.abc import Iterable
+from typing import Any, overload
 
 from docutils.transforms import Transformer
 
@@ -10,7 +12,26 @@ class Node:
     def __getattr__(self, __name: str) -> Any: ...  # incomplete
 
 class Element(Node):
+    children: list[Node]
     def __init__(self, rawsource: str = ..., *children: Node, **attributes): ...
+    def __len__(self) -> int: ...
+    def __contains__(self, key: str | Node) -> bool: ...
+    @overload
+    def __getitem__(self, key: str) -> Any: ...
+    @overload
+    def __getitem__(self, key: int) -> Node: ...
+    @overload
+    def __getitem__(self, key: slice) -> list[Node]: ...
+    @overload
+    def __setitem__(self, key: str, item: Any) -> None: ...
+    @overload
+    def __setitem__(self, key: int, item: Node) -> None: ...
+    @overload
+    def __setitem__(self, key: slice, item: Iterable[Node]) -> None: ...
+    def __delitem__(self, key: str | int | slice) -> None: ...
+    def __add__(self, other: list[Node]) -> list[Node]: ...
+    def __radd__(self, other: list[Node]) -> list[Node]: ...
+    def __iadd__(self: Self, other: Node | Iterable[Node]) -> Self: ...
     def __getattr__(self, __name: str) -> Any: ...  # incomplete
 
 class Structural: ...