[3.12] gh-88516: show file proxy icon in IDLE editor windows on macOS (GH-112894...

[3.12] gh-88516: show file proxy icon in IDLE editor windows on macOS (GH-112894) (#115840)

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.

(cherry picked from commit b48101864c724a7eab41a6878a836f38e54e04fb)

Co-authored-by: Ronald Oussoren <ronaldoussoren@mac.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>