add types to tkinter.filedialog.ask*

[Akuli]

Fixes #5571

The options are documented in tk_getOpenFile and tk_getSaveFile manual page (they are both in the same manual page), but to figure out which options actually apply, it turns out to be easiest to give an invalid option:

>>> import tkinter.filedialog
>>> tkinter.filedialog.askopenfilename(lol="wat")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/tkinter/filedialog.py", line 375, in askopenfilename
    return Open(**options).show()
  File "/usr/lib/python3.7/tkinter/commondialog.py", line 43, in show
    s = w.tk.call(self.command, *w._options(self.options))
_tkinter.TclError: bad option "-lol": must be -defaultextension, -filetypes, -initialdir, -initialfile, -multiple, -parent, -title, or -typevariable

[Akuli]

During several years of tkinter, I haven't seen anyone actually using these functions. They ask the file name, just like askopenfilename() or asksaveasfilename() or askopenfilenames() would, and pass it to the built-in open() function. When using these functions, it's not possible to pass other arguments to open(), such as encoding or errors.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉