[3.13] gh-151678: Add tests for tkinter.ttk methods (GH-151736) (GH-151743)

[3.13] gh-151678: Add tests for tkinter.ttk methods (GH-151736) (GH-151743)

Cover previously-untested ttk methods:

* Progressbar.step, start and stop;
* Treeview.parent, next, prev, see and identify_element;
* Style.theme_settings;
* OptionMenu.set_menu.
(cherry picked from commit 7d4a0aad7be3cfb367b8977a03a64e754577d5f0)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
* Fix regex in tests.

---------

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>