Fix add/remove event listeners in core:sys/wasm

[JonathanTron]

There were multiple issues here:

1. listeners stored in the same key overwriting the previous one
2. missing use_capture parameter in remove_event_listener/remove_window_event_listener

The key used to store the listener function in listenerMap was a javascript Object, when used as a key it was thus serialized to the string "[object Object]", meaning all listeners where effectively set to the same key when calling add_event_listener/add_window_event_listener. Later on when calling remove_event_listener/remove_window_event_listener, it then tried to remove the incorrect one or none at all if there was a mix of the same event name registered on an element or the window.

To fix I implemented a function listener_key in the javascript code which will generate a different key based on the event's:

• id: dom element's id or 'window' (when event listener added to the window)
• name: the event name (eg: click), each event handler should be removed for the event name it was register on.
• data: we can register events with different data, each one generate a new listener which has to be removed.
• callback: same as data, if you register two similar handler but with two different callback, each one should be removed.
• useCapture: this one is a bit tricky, but when you register an event handler in javascript, if you don't pass useCapture, it defaults to false. When you remove an handler, you have to pass the exact same useCapture option you registered it with. In this case, we allowed to register an event with different useCapture, but didn't allow to pass the useCapture when removing it. We always called removeEventListener without the useCapture parameter which removed the handler properly only when it was registered with useCapture=false.

I also switched the WasmMemoryInterface.listenerMap from {} (javascript object) to a new Map(), which is available everywhere nowadays.