fix(combobox): address multiselectable state issues with new TagGroup component

[jzempel]

Description

Addresses some touchy expand/collapse state bugs for multiselectable tag groups. The TagGroup is an internal-only component that renders a list of Tag components and {children} (the StyledTagsButton) as a final sibling.

Detail

Also shimmed in:

• an input aria-labelledby label readout hack for screenreaders
• preventing double readout of isEditable={false} combobox value

Checklist

• 👌 design updates will be Garden Designer approved (add the designer as a reviewer)
• 🌐 demo is up-to-date (yarn start)
• ⬅️ renders as expected with reversed (RTL) direction
• 🤘 renders as expected with Bedrock CSS (?bedrock)
• 💂‍♂️ includes new unit tests. Maintain existing coverage (always >= 96%)
• ♿ tested for WCAG 2.1 AA accessibility compliance
• 📝 tested in Chrome, Firefox, Safari, and Edge

[coveralls]

coverage: 95.491% (+0.004%) from 95.487% when pulling f277056 on jzempel/fix-tag-group into bcafe87 on main.

[geotrev]

Nothing major here, just questions mainly. The interactions feel much better. Making the tags all visible on focus is a great workaround!