Notifications: auto dismiss missing focusin/focusout events

[agjohnson]

Raising this as an issue, I commented on the PR here after it was merged. I didn't want this to get lost.

#375 (comment)

I had originally mentioned adding mouse and focus events to pause auto dismiss there. The focus events can be used by screen readers in the same way mouseover works for pointers. This also should cover keyboard focus.

[humitos]

We should probably take a look at how is the tab/keyboard order for these element. I'm not sure you are able to "focusin" the notification with the keyboard currently. I guess this is also related with accessibility too.

If you go to https://docs.readthedocs.io/en/latest/ and hit TAB multiple times, it does nothing. I'm not sure where the focus is, but I'm not able to move around the page with the keyboard. However, if you click on the content of the page and start hitting TAB, eventually, you will arrive at the notification.