[3.12] gh-112898: warn about unsaved files when quitting IDLE on macOS (GH-112939) (#112960)

gh-112898: warn about unsaved files when quitting IDLE on macOS (GH-112939)

* gh-112898: warn about unsaved files when quitting IDLE on macOS

Implement the TK function ``::tk::mac::Quit`` on macOS to
ensure that IDLE asks about saving unsaved files when
quitting IDLE.

(cherry picked from commit 3251ba8f1af535bf28e31a6832511ba19e96b262)


Co-authored-by: Christopher Chavez chrischavez@gmx.us

Co-authored-by: Ronald Oussoren <ronaldoussoren@mac.com>