Use raw Wiki links for non-renderable Wiki files (#30273)

Use raw Wiki links for non-renderable Wiki files (#30273)

In Wiki pages, short-links created to local Wiki files were always
expanded as regular Wiki Links. In particular, if a link wanted to point
to a file that Gitea doesn't know how to render (e.g, a .zip file), a
user following the link would be silently redirected to the Wiki's home
page.

This change makes short-links* in Wiki pages be expanded to raw wiki
links, so these local wiki files may be accessed without manually
accessing their URL.

* only short-links ending in a file extension that isn't renderable are
affected.

Closes #27121.

Signed-off-by: Rafael Girão <rafael.s.girao@tecnico.ulisboa.pt>
Co-authored-by: silverwind <me@silverwind.io>