[Fluent theme] Fix files and default exports

[compulim]

Changelog Entry

Added

• (Experimental) Added botframework-webchat-fluent-theme package for applying Fluent UI theme to Web Chat, by @compulim and @OEvgeny, in PR #5120
  • Fixed botframework-webchat-fluent-theme/package.json to export *.d.[m]ts and default exports, in PR #5131

Description

Files that need to be exported in the package.json should be included in the package.json/files.

Also, default exports should point to valid file.

Design

Specific Changes

• Updated packages/fluent-theme/package.json
  • Added *.d.[m]ts to files so it is packed correctly
  • Fixed main/types field so it is pointing to correct files

• 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)