Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/tkinter/dnd.pyi

@@ -0,0 +1,13 @@
+from _typeshed.tkinter import DndSource
+from tkinter import Event, Misc, Tk
+from typing import ClassVar, Optional
+
+class DndHandler:
+    root: ClassVar[Optional[Tk]]
+    def __init__(self, source: DndSource, event: Event[Misc]) -> None: ...
+    def cancel(self, event: Optional[Event[Misc]] = ...) -> None: ...
+    def finish(self, event: Optional[Event[Misc]], commit: int = ...) -> None: ...
+    def on_motion(self, event: Event[Misc]) -> None: ...
+    def on_release(self, event: Event[Misc]) -> None: ...
+
+def dnd_start(source, event) -> Optional[DndHandler]: ...