Event: Make focus re-triggering not focus the original element back

Event: Make focus re-triggering not focus the original element back

If during a focus handler another focus event is triggered:

```js
elem1.on( "focus", function() {
	elem2.trigger( "focus" );
} );
```

due to their synchronous nature everywhere outside of IE the hack added in
gh-4279 to leverage native events causes the native `.focus()` method to be
called last for the initial element, making it steal the focus back. Since
the native method is already being called in `leverageNative`, we can skip that
final call.

This aligns with changes to the `_default` method for the `click` event that
were added when `leverageNative` was introduced there.

A side effect of this change is that now `focusin` will only propagate to the
document for the last focused element. This is a change in behavior but it also
aligns us better with how this works with native methods.

Fixes gh-4382
Closes gh-4813
Ref gh-4279