support widgets in _TextIndex (#4954)

fixes #4953

Author: Akuli

stdlib/3/tkinter/__init__.pyi

@@ -2314,7 +2314,7 @@ class Scrollbar(Widget):
     def get(self): ...
     def set(self, first, last): ...
 
-_TextIndex = Union[_tkinter.Tcl_Obj, str, float]
+_TextIndex = Union[_tkinter.Tcl_Obj, str, float, Misc]
 
 class Text(Widget, XView, YView):
     def __init__(