DEV: Upgrading Discourse to Zeitwerk (#8098)

Zeitwerk simplifies working with dependencies in dev and makes it easier reloading class chains. 

We no longer need to use Rails "require_dependency" anywhere and instead can just use standard 
Ruby patterns to require files.

This is a far reaching change and we expect some followups here.

app/helpers/application_helper.rb

@@ -2,14 +2,6 @@
 # frozen_string_literal: true
 require 'current_user'
 require 'canonical_url'
-require_dependency 'guardian'
-require_dependency 'unread'
-require_dependency 'age_words'
-require_dependency 'configurable_urls'
-require_dependency 'mobile_detection'
-require_dependency 'category_badge'
-require_dependency 'global_path'
-require_dependency 'emoji'
 
 module ApplicationHelper
   include CurrentUser