collections: Add missing reflected BinOp methods (#7207)

Co-authored-by: Jelle Zijlstra <[email protected]>

stdlib/collections/__init__.pyi

@@ -94,8 +94,10 @@ class UserList(MutableSequence[_T]):
     def __setitem__(self, i: slice, o: Iterable[_T]) -> None: ...
     def __delitem__(self, i: SupportsIndex | slice) -> None: ...
     def __add__(self: Self, other: Iterable[_T]) -> Self: ...
+    def __radd__(self: Self, other: Iterable[_T]) -> Self: ...
     def __iadd__(self: Self, other: Iterable[_T]) -> Self: ...
     def __mul__(self: Self, n: int) -> Self: ...
+    def __rmul__(self: Self, n: int) -> Self: ...
     def __imul__(self: Self, n: int) -> Self: ...
     def append(self, item: _T) -> None: ...
     def insert(self, i: int, item: _T) -> None: ...
@@ -129,8 +131,15 @@ class UserString(Sequence[UserString]):
     def __iter__(self: Self) -> Iterator[Self]: ...
     def __reversed__(self: Self) -> Iterator[Self]: ...
     def __add__(self: Self, other: object) -> Self: ...
+    def __radd__(self: Self, other: object) -> Self: ...
     def __mul__(self: Self, n: int) -> Self: ...
+    def __rmul__(self: Self, n: int) -> Self: ...
     def __mod__(self: Self, args: Any) -> Self: ...
+    if sys.version_info >= (3, 8):
+        def __rmod__(self: Self, template: object) -> Self: ...
+    else:
+        def __rmod__(self: Self, format: Any) -> Self: ...
+
     def capitalize(self: Self) -> Self: ...
     def casefold(self: Self) -> Self: ...
     def center(self: Self, width: int, *args: Any) -> Self: ...