BasicTranscript: improve focus display

[OEvgeny]

Fixes #

Changelog Entry

Fixed

• Fixes #5146. Fixed chat history focus indicator should not show up on tap, by @OEvgeny, in PR #5145

Description

Use the focus-visible selector, so browser can use built-in heuristics to determine if they should display the focus ring or not.

Design

We intentionally do not specify the :focus selector letting older browser to use native styles. This should work out as the most browsers support the :focus-visible selector:

Specific Changes

• Modified StyleSet/BasicTranscript.tsx to use :focus-visible instead of :focus to show the focus indicator

• 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)

[OEvgeny]

I intentionally left :focus pseudo-class at the line 103 as it serves the different purpose of hiding content when focus present, and should work regardless focus-visible support.