Add semi-support for Video/Image objects in ActivityPub (#5848)

* Add semi-support for Video/Image objects in ActivityPub

Video and Image objects will create corresponding status records
with manually crafted text contents (title + URL)

* Extract html-url-finding logic into JsonLdHelper

* Fallback to id when url missing, extract supported object types

app/helpers/jsonld_helper.rb

@@ -9,6 +9,24 @@ module JsonLdHelper
     value.is_a?(Array) ? value.first : value
   end
 
+  # The url attribute can be a string, an array of strings, or an array of objects.
+  # The objects could include a mimeType. Not-included mimeType means it's text/html.
+  def url_to_href(value, preferred_type = nil)
+    single_value = if value.is_a?(Array) && !value.first.is_a?(String)
+                     value.find { |link| preferred_type.nil? || ((link['mimeType'].presence || 'text/html') == preferred_type) }
+                   elsif value.is_a?(Array)
+                     value.first
+                   else
+                     value
+                   end
+
+    if single_value.nil? || single_value.is_a?(String)
+      single_value
+    else
+      single_value['href']
+    end
+  end
+
   def as_array(value)
     value.is_a?(Array) ? value : [value]
   end