Add "selected" section to IDLE Statusbar

IDLE statusbar shows the current line-column info of cursor. This is helpful for quickly finding out where the cursor is. It would also be helpful to show number of characters selected in the editor, in the statusbar. Modern text editors like vscode also show how many characters are selected in the editor. Add this feature to IDLE.

• This label should be hidden if no character is selected.
• This should be updated everytime the line-col info updates

Example

Linked PRs

• gh-92822: IDLE - Add a selection label to window statusbars #92823