Add MacOS menu (#1583)

* feat: added MacOS menu

* fix: ran fmt

* extracted function into variable

* idiomatic formatting

* Set the default menu only during app startup

* Don't set the activation policy in the menu init

Co-authored-by: Artur Kovacs <kovacs.artur.barnabas@gmail.com>

src/platform_impl/macos/mod.rs

@@ -7,6 +7,7 @@ mod app_state;
 mod event;
 mod event_loop;
 mod ffi;
+mod menu;
 mod monitor;
 mod observer;
 mod util;