Skip hidden dropdowns while focusing

[jeremyvii]

This PR fixes issue #29405 by filtering out dropdown items set to display: none when focusing between items. The isVisible() utility method filters out the hidden items.

[patrickhlauke]

not had a chance to test, but i'll just throw out that you might also need to check for visible, but disabled, ones as well

[jeremyvii]

I think disabled items are ignored per this dropdown selector here, but I will double check.

[Johann-S]

Hi @jeremyvii,

Thanks for your PR!
Can you add a unit test please ?

[jeremyvii]

While adding this unit test, I had noticed that isVisible() doesn't account for the d-none class. I added a check for this class in isVisible().

[jeremyvii]

I was just reviewing the change I made, and think it may be better to use getComputedStyle() for checking if an element is hidden. Rather than checking for the d-none class explicitly. That way if a user has some rouge class that hides an element it will still be skipped while focusing between items.