Add __all__ for modules beginning with 'c' and 'd' (#7303)

stdlib/difflib.pyi

@@ -4,6 +4,21 @@ from typing import Any, AnyStr, Callable, Generic, Iterable, Iterator, NamedTupl
 if sys.version_info >= (3, 9):
     from types import GenericAlias
 
+__all__ = [
+    "get_close_matches",
+    "ndiff",
+    "restore",
+    "SequenceMatcher",
+    "Differ",
+    "IS_CHARACTER_JUNK",
+    "IS_LINE_JUNK",
+    "context_diff",
+    "unified_diff",
+    "diff_bytes",
+    "HtmlDiff",
+    "Match",
+]
+
 _T = TypeVar("_T")
 
 class Match(NamedTuple):