Improve editor open URL command to open the selected portion of URL (#21825)

Closes #21718

Just like in Vim, if a URL is selected, it opens exactly that portion of
the URL. Otherwise, if only the cursor is on a URL, it opens the entire
URL.

Zed currently does the latter. This PR also adds support for the former.


https://github.com/user-attachments/assets/8bdd2952-ceec-487c-b27a-5cea4258eb03

Release Notes:

- Updated the `editor: open url` to also handle the selected portion of
a URL.