[3.11] gh-68166: Tkinter: Add tests and examples for element_create() (GH-111453) (GH-111858)

* Remove mention of "vsapi" element type from the documentation.
* Add tests for element_create() and other ttk.Style methods.
* Add examples for element_create() in the documentation.

(cherry picked from commit 005d1e8fc81539c60c6b21ebba34de3edd5bb232)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>