Remove bogus aria-labelledby

[compulim]

Fixes #3676.

Changelog Entry

Fixed

• Fixes #3676. Activities without text should not generate bogus aria-labelledby, by @compulim in PR #3697

Description

When we render an activity without text content, the aria-labelledby is not needed because it is referencing to the text content which does not exists.

Design

The aria-labelledby is added for accessibility, but in some cases, such as activity without text content, we don't need it. And it's also violating accessibility if we set aria-labelledby without a corresponding element.

Specific Changes

• Modify StackedLayout.js not to inject the aria-labelledby if not needed
• Added tests

• 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)