browserTrigger doesn't support keydown with a specific keycode

[jintoppy]

if I do browserTrigger(element, 'keydown'), there is no option to give keyCode. It is going to line 127, to initMouseEvent, even though this is a keydown event.

[caitp]

Personally I don't think this would be too bad, since it's not included in production code anyways --- my vote is PRs welcome.

[gonzaloruizdevilla]

For PR #10193 I had to do exactly this.

I had to make two different commits:
gonzaloruizdevilla@2f0d4fb to allow key events
gonzaloruizdevilla@d70e0d4 to force artificially event bubbling in trees detached from the document (bubbling don't work in these cases in some browsers like chrome)