DEV: Make discourse-common an Ember addon. (#9578)

This is to help with the migration to Ember CLI. In the current running
version of Discourse everything should be the same as before, just with
a few extra files that are not used. However, using Ember CLI this can
be installed as an Ember addon.

Co-Authored-By: Jarek Radosz <jradosz@gmail.com>

lib/discourse_js_processor.rb

@@ -161,7 +161,7 @@ JS
       end
 
       # We need to strip the app subdirectory to replicate how ember-cli works.
-      path || logical_path&.gsub('app/', '')
+      path || logical_path&.gsub('app/', '')&.gsub('addon/', '')
     end
 
   end