DEV: Replace custom Onebox blank implementation with ActiveSupport (#23827)

We have a custom implementation of #blank? in our Onebox helpers. This is likely a legacy from when Onebox was a standalone gem. This change replaces all usages with respective incarnations of #blank?, #present?, and #presence from ActiveSupport. It changes a bunch of "unless blank" to "if present" as well.

lib/onebox/engine/facebook_media_onebox.rb

@@ -25,8 +25,7 @@ module Onebox
           HTML
         else
           html = Onebox::Engine::AllowlistedGenericOnebox.new(@url, @timeout).to_html
-          return if Onebox::Helpers.blank?(html)
-          html
+          html.presence
         end
       end
     end