[FR] Add option to specify a base URL when calling the |anchors filter

[rungta]

Description

Typical behaviour for anchor links are to act as permalinks to a heading on a page. Currently the links generated are relative to the current page, which may or may not be the permalink page for that entry. So it would be great if there was an optional parameter on the |anchors filter for specifying the base URL which can be prepended to all generated anchor links.

<!-- current behavior -->
<a class="anchor" href="#foo-bar" … >
  #
</a>

<!-- with a new base URL param -->
<a class="anchor" href="https://example.com/blog/2023/entry-permalink#foo-bar" … >
  #
</a>

Steps to reproduce

1. Create a blog index page and show the latest 5 entries on that page.
2. For each blog teaser on the index page, show the full post text, generate anchor links on the headings in the post.
3. The generated link for all headings will be relative to the blog index page, not the blog entry’s permalink page. So the links will stop working once the current posts are replaced with newer posts in the index.

Additional info

• Craft version: 4.3.10
• PHP version: 8.0
• Plugins & versions: 3.2.0