External Link Icons to distinguish internal from external hyperlinks in wiki text

Description

No easy way for users to tell if a hyperlink on a wiki is internal or external. Would like to see an icon following external links, similar to MediaWiki.

Proposal

MediaWiki-style icons by external links would be helpful to allow users to differentiate internal and external links within the wiki text. As shown on https://en.wikipedia.org/wiki/Help:External_link_icons they distinguish both by url scheme and file extension. Just indicating external links is highest value to me, but it could be useful to show file type icons (particularly for pdf) as well.

Links / references

Possibly related to issue #2705 (moved), but this request refers to individual links within the wiki.

Documentation blurb

Overview

What is it? Why should someone use this feature? What is the underlying (business) problem? How do you use this feature?

Use cases

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Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.