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.

spec/components/validators/upload_validator_spec.rb

@@ -1,9 +1,8 @@
 # frozen_string_literal: true
 
 require 'rails_helper'
-require_dependency 'validators/upload_validator'
 
-describe Validators::UploadValidator do
+describe UploadValidator do
   subject(:validator) { described_class.new }
 
   describe 'validate' do