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/include.html

@@ -11,7 +11,7 @@
 	{{- .Content | safeHTML -}}
 	{{- else -}}
 	{{/* It is not a resource in the includes bundle. Try to find the page relative to the current. */}}
-	{{- $path := path.Join $.Page.Dir $name -}}
+	{{- $path := path.Join $.Page.File.Dir $name -}}
 	{{- $page := site.GetPage "page" $path -}}
 	{{- with $page }}
 	{{ .Content }}