Make it compatible with Hugo 0.55 (#13680)

This commit adds two backwards compatible changes to prepare for the next Hugo version, most notable:

* All the `File` methods on `Page` has been deprecated and will give a warning in the next Hugo version. Adjust this by changing `.Dir` to ´.File.Dir` and similar.
* Version the capture shortcode to use the old behaviour for markdown rendering of shortcode inner content.

layouts/shortcodes/code.html

@@ -2,8 +2,8 @@
 {{ $file := .Get "file" }}
 {{ $codelang := .Get "language" | default (path.Ext $file | strings.TrimPrefix ".") }} 
 {{ $fileDir := path.Split $file }}
-{{ $bundlePath := path.Join .Page.Dir $fileDir.Dir }}
-{{ $filename := path.Join $p.Dir $file }}
+{{ $bundlePath := path.Join .Page.File.Dir $fileDir.Dir }}
+{{ $filename := path.Join $p.File.Dir $file }}
 {{ $ghlink := printf "https://%s/blob/master/content/%s/%s" site.Params.githubwebsiterepo .Page.Lang $filename | safeURL }}
 {{/* First assume this is a bundle and the file is inside it. */}}
 {{ $resource := $p.Resources.GetMatch (printf "%s*" $file ) }}