Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/tkinter/commondialog.pyi

@@ -0,0 +1,8 @@
+from typing import Any, ClassVar, Mapping, Optional
+
+class Dialog:
+    command: ClassVar[Optional[str]] = ...
+    master: Optional[Any] = ...
+    options: Mapping[str, Any] = ...
+    def __init__(self, master: Optional[Any] = ..., **options) -> None: ...
+    def show(self, **options) -> Any: ...