Add support for keyboard via a @useFocus argument

[Pjaerr]

Adds a @useFocus argument to the tooltip component (off by default) to allow showing the tooltip when a user focuses the tooltipper instead of this only being available to mouse users.

Previously this would be handled in the code of an app that uses the addon by wrapping the tooltip and manually showing/hiding it based on focus/blur events.

Added tests around the show arg as I accidentally broke this behaviour but tests didn't catch it.

Areas for review

General thoughts +

• Does it make sense to combine the event listeners for mouse/keyboard? (ie. just use a single handler and isOverTooltipper variable), and then whether or not keyboard is supported would be handled purely by whether or not the event listeners have been added or not

• Have I missed any places worth testing?

[Pjaerr]

@amk221 I've had a quick crack at this in favour of creating a wrapper component and handling in our app. Happy to go that way though if preferred.

Absolutely no rush to take a look at this, only if you get a moment!

[Pjaerr]

@amk221 I did want to use the focus/blur test helpers here but I'm really not sure why it causes the test to fail due to the tooltip not being hidden.

I wonder, could it be something to do with the fact that the focus/blur helpers actually fire focus -> focusin / blur -> focusout so potentially the order of events ends up being mixed, meaning we end up with the last event being a focus event, not a blur event. triggerEvent works as expected, I’ve updated the main focusing test to also blur, ensuring the focusing behaviour is working.