gh-43457: Tkinter: fix design flaws in wm_attributes() (GH-111404)

* When called with a single argument to get a value, it allow to omit
  the minus prefix.
* It can be called with keyword arguments to set attributes.
* w.wm_attributes(return_python_dict=True) returns a dict instead of 
  a tuple (it will be the default in future).
* Setting wantobjects to 0 no longer affects the result.