Carbon: Add listbox components to public API

[joshblack]

We currently have several internal components that we use to build up our dropdowns, including:

• ListBox
• ListBoxField
• ListBoxMenu
• ListBoxMenuItem
• ListBoxMenuIcon
• ListBoxSelection

It would be helpful to update these, make sure they're good to go, and then add them as part of our public API. This would be helpful so teams could build out dropdown-variants using the look and feel of our components without necessarily having to use the behavior.

Looking forward, this may be the recommended strategy in conjunction with downshift so we don't leak library details through the public API of our components.

[sonarestis]

Writing with a personal email, but my team in IBM from Ottawa, Canada would really appreciate if the components above are exposed. Saves us time from reimplementing the wheel!

[PaulJThompson]

+1 it would be super-helpful if these were exposed.

[dan-cooke]

This would be incredibly useful, as the import from lib directly seems to break tree shaking of icons react.

This is the only lib import in our entire, app we are most likely going to have to copy the source code for the ListBox component into our repo in the meantime.