Investigate accessibility issues of React Select

[johnbillion]

Unfortunately we weren't able to use Reach UI Combobox as it doesn't support multiple selection.

Some cursory Googling tells us that React Select by default has some accessibility issues. These need to be tested, listed, and then investigated.

[johnbillion]

It seems the a11y issues with React Select are quite pervasive. While it is fully keyboard accessible, its controls are not particularly intuitive and there are many ARIA issues relating to the <div> soup and mouse-first approach to its controls.

At this point I am considering switching to a component that treats accessibility as a first-class citizen instead of an after-thought, despite the work already put into implementing React Select.

Previously: #7

• Downshift looks the most promising so far, it supports multiple selection and creation, but it does not provide rendering out of the box. Plenty of examples to use as a basis though.
• Reach UI focuses on a11y but does not appear to support multiple selection.

[johnbillion]

Mentioned by Thorsten is the built-in tag component in Gutenberg, FlatTermSelector. Needs looking in to.