Suggested actions image alt text fallback

[compulim]

Related to #4333.

Changelog Entry

Fixed

• Card action image alt text should use imageAltText field and fallback to text field, by @compulim in PR #4333

Description

Image on suggested actions should have alt text from imageAltText field, and fallback to text field.

Today, we support imageAltText field only. And did not fallback to text field.

This pull request will enable image alt text fallback using text field.

Specific Changes

• Updated <SuggestedActions> to fallback to text field

• 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)