Improve accessibility on Edge Chromium

[compulim]

Fixes #3570.

Changelog Entry

Fixed

• Fixes #3570. Adaptive Card speak property should be narrated by screen reader, by @compulim in PR #3573 and PR #3584

Description

Improves live region attachments labelling work in #3573 for Edge Chromium.

Tested on:

• Microsoft Edge (Chromium) + Windows Narrator
• Microsoft Edge (UWP) + Windows Narrator
• Chrome on Windows + NVDA
• Firefox on Windows + NVDA
• macOS Safari + VoiceOver
• iOS Safari + VoiceOver
• Chrome on Android + TalkBack

Design

Today

<article>
  <div role="region">An image</div>
</article>

Tomorrow

<article aria-labelledby="a1b2c">
  <div id="a1b2c">An image</div>
</article>

Specific Changes

• Modified all live region attachment middleware with the updated DOM tree

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)

[corinagum]

LGTM

Side note: I think the attachment strings are a little clunky. Can we go over them sometime in R12?