a11y: improve batch change detail page

Created by: LawnGnome

This came out of the audit for #34081 (closed). The changes are basically in two categories:

1. Elements that don't work well with screen readers: either aria-label attributes or elements with sr-only classes have been added as appropriate, and some text strings have been combined at the TypeScript level so they appear as one DOM node instead of multiple.
2. Addressed some ARC Toolkit issues.

Test plan

Storybook coverage will handle any unintended visual changes, otherwise testing used my eyes and ears.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.