Change RSS feeds (#18356)

* Change RSS feeds

- Use date and time for titles instead of ellipsized text
- Use full content in body, even when there is a content warning
- Use media extensions

* Change feed icons and add width and height attributes to custom emojis

* Fix custom emoji animate on hover breaking

* Fix tests

app/lib/rss/media_content.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class RSS::MediaContent < RSS::Element
+  def initialize(url, type, size)
+    super()
+
+    @root = create_element('media:content') do |content|
+      content['url']      = url
+      content['type']     = type
+      content['fileSize'] = size
+    end
+  end
+
+  def medium(str)
+    @root['medium'] = str
+  end
+
+  def rating(str)
+    append_element('media:rating', str) do |rating|
+      rating['scheme'] = 'urn:simple'
+    end
+  end
+
+  def description(str)
+    append_element('media:description', str) do |description|
+      description['type'] = 'plain'
+    end
+  end
+end