fix(web-components): add missing export for AnchorButtonStyles

[motss]

Checklist

✅ Code is up-to-date with the master branch
✅ yarn change
✅ yarn prerelease
✅ yarn build

Previous Behavior

#33957 missed updating src/index.ts to export AnchorButtonStyles.

import { AnchorStyles } from '@fluentui/web-components';

// '"@fluentui/web-components"' has no exported member named 'AnchorButtonStyles'. Did you mean 'ButtonStyles'?ts(2724)

New Behavior

This PR addresses that oversight, allowing AnchorButtonStyles to be imported directly from @fluentui/web-components.

import { AnchorStyles } from '@fluentui/web-components'; // no ts error

Related Issue(s)

1. Fixes oversight in fix: export AnchorButtonStyles in its index.ts #33957.