Add tkinter wrappers for Menu postcascade and the tk scaling and tk inactive commands

[serhiy-storchaka]

A few long-standing Tk commands have no tkinter wrapper and are currently reachable only through tk.call().

• The menu postcascade command (since Tk 8.5) posts the submenu of a cascade entry, complementing the already wrapped post and unpost.
• tk scaling (since Tk 8.4) queries or sets the scaling factor (pixels per point) used to convert between physical units and pixels.
• tk inactive (since Tk 8.5) returns the time in milliseconds since the user last interacted with the system, and can reset that timer.

I propose to add the corresponding Menu.postcascade(), Misc.tk_scaling() and Misc.tk_inactive() methods.

Linked PRs

• gh-151881: Add tkinter Menu.postcascade, Misc.tk_scaling and tk_inactive #151882