gh-127930: use explicit imports in tkinter.simpledialog

[tungol]

simpledialog was overlooked when all the other tkinter submodules were updated to use explicit imports in #14864. This MR fixes that.

This is relevant to typeshed, where stubtest detects the extra constants imported into tkinter.simpledialog and emits a warning that they're not present in the stubs. Star imports in the stdlib usually indicate an intention to re-export.

I don't think this is user-facing enough to need a NEWS entry, but I'm happy to add one if anyone thinks otherwise.

• Issue: Explicit imports in tkinter.simpledialog #127930

[picnixz]

I hope, no one does from tkinter.simpledialog import SOMETHING_THAT_WAS_STAR_IMPORTED or from tkinter.simpledialog import *. Otherwise, LGTM. What you can do is perhaps add a __all__ for this module? (in which case, you should perhaps have a NEWS entry).

[tungol]

I added __all__. All the other tkinter.* submodules have one, so that keeps this consistent.