gh-151881: Add tkinter Menu.postcascade, Misc.tk_scaling and tk_inactive (GH-151882)

gh-151881: Add tkinter Menu.postcascade, Misc.tk_scaling and tk_inactive (GH-151882)

Wrap three long-standing Tk commands that had no tkinter wrapper:

* Menu.postcascade() posts the submenu of a cascade entry (Tk 8.5),
  complementing the existing post() and unpost() methods.
* Misc.tk_scaling() queries or sets the scaling factor in pixels per
  point used to convert between physical units and pixels (Tk 8.4).
* Misc.tk_inactive() returns the user idle time in milliseconds, and can
  reset that timer (Tk 8.5).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>