Add missing tkinter submodules (#4558)

Co-authored-by: Akuli <akuviljanen17@gmail.com>

stdlib/2and3/_typeshed/tkinter.pyi

@@ -0,0 +1,7 @@
+import sys
+from typing import Optional, Protocol
+
+if sys.version_info >= (3,):
+    from tkinter import Event, Misc, Widget
+    class DndSource(Protocol):
+        def dnd_end(self, target: Optional[Widget], event: Optional[Event[Misc]]) -> None: ...