add LinkText and underline to HC button-link

[beyackle2]

Fixes ADO issue 15603122 (https://msazure.visualstudio.com/CCI/_workitems/edit/15603122)

Changelog Entry

Fixed

• Fixes #4558. In high contrast mode, "Retry" link button should use link color as defined by CSS System Colors, by @beyackle2 in PR #4537

Description

High-contrast themes like Desert and Aquatic render button text in the same color as ordinary text. This is a problem when we use a button to mimic a link (as we do in InlineMarkdown), because then the text blends into the surrounding text.

Specific Changes

This adds a @media forced-colors selector to InlineMarkdown that adds the semantic LinkText color and a single underline to links that have been turned from Markdown into buttons; this makes them visually distinct.

[in draft until there are unit 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)