Use MessageEvent in EventSource#addEventListener

[Alexendoo]

Fixes #736

The event listeners are removed and then recreated to avoid having the
existing add/removeEventListeners in addition to the new ones

[ghost]

All CLA requirements met.

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[saschanaz]

This is redefining too many things. Since this case is special enough I would just hardcode the event type in the function generating addEventListener.

If you prefer not to hardcode, you can maybe add some field defaultEventInterface and use that.

[Alexendoo]

Thanks, made that change. That is nicer indeed

[saschanaz]

Hmm, this potentially breaks compatibility with { handleEvent: () =>{} }. Could you add another signature that accepts EventListenerObject, and add a unit test in unittests/files/?

[Alexendoo]

Yeah you're right. I thought it would take the definition from the extends EventTarget. I'll make it purely additive

[saschanaz]

Looks great, thank you! Just waiting for the tests to pass...

[saschanaz]

LGTM

[github-actions]

Merging because @saschanaz is a code-owner of all the changes - thanks!