Use the CloseWatcher API to track native modal closes in GA

[chrisblakley]

CloseWatcher API documentation:

• https://html.spec.whatwg.org/multipage/interaction.html#the-closewatcher-interface
• https://close-watcher-demo.glitch.me/

Here is an example of how to use it:

Probably something like this:

const watcher = new CloseWatcher();
watcher.addEventListener('close', function(){
    //Send GA4 event here for element close
});