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/allowed_ip_address_validator.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require_dependency "spam_handler"
-
 class AllowedIpAddressValidator < ActiveModel::EachValidator
 
   def validate_each(record, attribute, value)

lib/validators/alternative_reply_by_email_addresses_validator.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'validators/reply_by_email_address_validator'
-
 class AlternativeReplyByEmailAddressesValidator
   def initialize(opts = {})
     @opts = opts

lib/validators/password_validator.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require_dependency "common_passwords/common_passwords"
-
 class PasswordValidator < ActiveModel::EachValidator
 
   def validate_each(record, attribute, value)

lib/validators/post_validator.rb

@@ -1,10 +1,6 @@
 # frozen_string_literal: true
 
-require_dependency 'validators/stripped_length_validator'
-
-module Validators; end
-
-class Validators::PostValidator < ActiveModel::Validator
+class PostValidator < ActiveModel::Validator
 
   def validate(record)
     presence(record)
@@ -51,7 +47,7 @@ class Validators::PostValidator < ActiveModel::Validator
       SiteSetting.post_length
     end
 
-    Validators::StrippedLengthValidator.validate(post, :raw, post.raw, range)
+    StrippedLengthValidator.validate(post, :raw, post.raw, range)
   end
 
   def raw_quality(post)

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

lib/validators/upload_validator.rb

@@ -4,7 +4,7 @@ require_dependency "file_helper"
 
 module Validators; end
 
-class Validators::UploadValidator < ActiveModel::Validator
+class UploadValidator < ActiveModel::Validator
 
   def validate(upload)
     # staff can upload any file in PM