Fix activity grouping for accessibility

[compulim]

Fixes #3133.

Changelog Entry

Fixed

• Fixes #3133. Associate ARIA labels with buttons in hero card and Adaptive Cards, by @compulim in PR #3146.
  • Remove browser-based detection from <ScreenReaderText> because it is no longer needed.
  • After stripping Markdown syntax for accessibility labels, cache the result to improve rendering performance.
  • Skip stripping Markdown for non-Markdown text content.

Description

When AT is reading Adaptive Card attachment, the label (<ScreenReaderText>) is not read correctly.

On top of this fix, we also need Adaptive Card bump that would remove tabindex="0' from their DOM node.

Specific Changes

Please refer to changelog above for specific changes.

---

• Testing Added
  • Manual testing steps are required
    1. Bot send 2 different hero cards (type herocard qna to MockBot)
       • The activity which contain the hero cards must have a text on it
       • The content of the hero card must have 2 card actions
    2. Launch Narrator or other AT
    3. Focus on the first button of first hero card
    4. Press TAB to focus to the first button of the second hero card
    5. Make sure AT read "Bot said, second activity text. Sent at ... First button"
    6. Press TAB to focus to the second button of the second hero card
    7. Make sure AT read "Second button"
    8. Press SHIFT + TAB to focus to the second button of the first hero card
    9. Make sure AT read "Bot said, first activity text. Sent at ... Second button"

[beyackle]

This all looks good. 🚢!