gh-88516: show file proxy icon in IDLE editor windows on macOS (#112894)

The platform standard on macOS is to show a proxy icon for open
files in the titlebar of Windows. Make sure IDLE matches this
behaviour.

Don't use both the long and short names in the window title.
The behaviour of other editors (such as Text Editor) is to show
only the short name with the proxy icon.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>