Deprecate and remove useFocusZone dependency array

[iansan5653]

useFocusZone accepts an uncommon optional second argument: an array of dependencies. While comparable to the dependency arrays passed to other React hooks, the optionality and unlinted nature of this argument make it easy to forget about or incorrectly configure. I have personally introduced a few bugs because I didn't know this argument needed to be considered.

I think with modern JavaScript this array is probably wholly unnecessary. All options passed to useFocusZone through the options object can easily be included as dependencies by using a shallow comparison. The trickier part is for the hook to know when the contents of the container element change, but this can now relatively easily be achieved by using a MutationObserver on the parent.

With MutationObserver, the dependencies array could be totally removed. This would simplify the API and clear up a potential footgun.

[lesliecdubs]

Thanks for filing, @iansan5653! Things are a bit quiet though the holidays, so I'm going to leave this in the Primer inbox to discuss with the team in the new year to see how we might be able to move this forward.