fix(multiselect): listbox hidden when closed

[jnm2377]

Closes #11341

Changelog

• make listbox menu hidden in the a11y tree when multiselect is closed

Testing / Reviewing

• go to multiselect storybook and run the a11y checker on the closed menu

  • this a11y warning should no longer appear
  

• ensure all tests are passing and component is working as expected

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[tw15egan]

I seem to be still seeing the issue when the Multiselect is open

Go to the MultiSelect default storybook
Open the MultiSelect (use inspect element on one of the entry to open DevTools without closing the menu)
Scan with IBM Equal Access Accessibility Checker (while the MultiSelect is opened)
You get the following accessibility violation:
2.1.1 Keyboard: The descendent <div> element with "option" role has no focusable child element

[jnm2377]

@tw15egan @dakahn this is ready for re-review. I added a tab index of -1 to the listbox menu item component bc the same accessibility error was present in Dropdown which also uses this component. ComboBox uses it as well, however, we added tabIndex -1 to that component so it wasn't failing a11y checker. So this change just adds it to all menu items by default. The components should all still work as expected.

[tw15egan]

Not seeing the violation anymore, nice work 🔥