dillon1000/react

Fix a regression that caused us to listen to extra events at the top (#12878)

* Rewrite to a switch

I find it a bit easier to follow than many comparison conditions.

* Remove unnecessary assignments

They are being assigned below anyway. This is likely a copypasta from the FOCUS/BLUR special case (which *does* need those assignments).

* Unify "cancel" and "close" cases

Their logic is identical.

* Don't listen to media events at the top

* Add a unit test for double-invoking form events

* Remove an unused case and document it in a test

The case I added was wrong (just like including this event in the top level list was always wrong).

In fact it never bubbles, even for <img>. And since we don't special case it in the <img> event
attachment logic when we create it, we never supported <img onLoadStart> at all.

We could fix it. But Chrome doesn't support it either: https://bugs.chromium.org/p/chromium/issues/detail?id=458851.
Nobody asked us for it yet. And supporting it would require attaching an extra listener to every <img>.

So maybe we don't need it? Let's document the existing state of things.

* Add a test verifying we don't attach unnecessary listeners

* Add a comment

* Add a test for submit (bubbles: false)