
Introduce a new class, EventEmitter, which implements signal handling for pure JavaScript classes. EventEmitter still utilizes GJS' addSignalMethods internally. EventEmitter allows static typechecking to understand the structure of event-emitting JS classes and makes creating child classes simpler. The name 'EventEmitter' mirrors a common name for this pattern in Node and in JS libraries. Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2043>