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.

lib/validators/stripped_length_validator.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
-module Validators; end
-class Validators::StrippedLengthValidator < ActiveModel::EachValidator
+class StrippedLengthValidator < ActiveModel::EachValidator
   def self.validate(record, attribute, value, range)
     unless value.nil?
       stripped_length = value.strip.length