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

config/locales/en.yml

@@ -1357,6 +1357,11 @@ en:
   reports:
     errors:
       invalid_rules: does not reference valid rules
+  rss:
+    content_warning: 'Content warning:'
+    descriptions:
+      account: Public posts from @%{acct}
+      tag: 'Public posts tagged #%{hashtag}'
   scheduled_statuses:
     over_daily_limit: You have exceeded the limit of %{limit} scheduled posts for today
     over_total_limit: You have exceeded the limit of %{limit} scheduled posts