creating data entries for remaining events on ticket 1123

[chrisdavidmills]

As per mdn/sprints#1123

This PR creates event data for:

https://developer.mozilla.org/en-US/docs/Web/API/Document/keydown_event
https://developer.mozilla.org/en-US/docs/Web/API/Document/keyup_event

https://developer.mozilla.org/en-US/docs/Web/API/Element/keydown_event
https://developer.mozilla.org/en-US/docs/Web/API/Element/keyup_event

https://developer.mozilla.org/en-US/docs/Web/API/EventSource/error_event
https://developer.mozilla.org/en-US/docs/Web/API/EventSource/message_event
https://developer.mozilla.org/en-US/docs/Web/API/EventSource/open_event

https://developer.mozilla.org/en-US/docs/Web/API/Window/offline_event
https://developer.mozilla.org/en-US/docs/Web/API/Window/online_event

The last two were a bit pathetic, I'm afraid. There is no existing on... data for them, as those pages don't yet exist, so for now I've just put in placeholder null values for them.

[chrisdavidmills]

paging mr @Elchi3 ; urgent data for tomorrow's release ;-)

[wbamberg]

The last two were a bit pathetic, I'm afraid. There is no existing on... data for them, as those pages don't yet exist, so for now I've just put in placeholder null values for them.

Some guy called Robert Nyman wrote this: https://robertnyman.com/html5/offline/online-offline-events.html. It's probably rubbish, but it seems to indicate that these events are supported in at least Firefox, Chrome (and presumably Chromealikes), and Safari.

Edited to add: there's also https://caniuse.com/#search=offline indicating that it's widely supported.

[chrisdavidmills]

Ah, thanks Will; looks good to me. I am happy for you to merge this.

[wbamberg]

Formally this looks fine, and the data makes sense (I think it could possibly replace some nulls, but copying the on- version is perfectly fine thing to do IMO).

I updated the data for offline and online since it seems pretty clear that these are widely supported.

Thanks @chrisdavidmills !