Add link to WP Repo in Theme Preview screen

[Guido07111975]

While searching for a theme at page wp-admin/theme-install.php you can click Details & Preview and a live preview opens.
Sometimes you want to learn more about the theme. This PR adds a link to the theme page in the WP Repo.

What's possible for plugins (View Details / WordPress.org Plugin Page ») should also be possible for themes.

Note: you can also reach the WP Repo via the ratings link, but that one does not link to the main theme page.

Trac ticket: #64905

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props guido07111975.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

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