[3.15] gh-150836: Mount embedded Tk ZIP in _tkinter on Windows (GH-151735)

[3.15] gh-150836: Mount embedded Tk ZIP in _tkinter on Windows (GH-151735)

Tcl/Tk 9 may embed the Tk script library in the Tk DLL on Windows. This embedded library is not found by Tcl by default.

Mount the loaded Tk DLL as a zipfs archive before calling Tk_Init(), so Tk can find its embedded tk_library using its existing library discovery logic.

Preserve Tk_Init()'s normal path if the library is not embedded.
(cherry picked from commit c4eb3adbb42d781e2ad35bee5621f1c621c6767b)

Co-authored-by: Jonathan J. Helmus <jjhelmus@gmail.com>