Support X_if_ee methods for QA tests

For the QA tests to use the new injection methods, we must require the
initializer and ensure that the "constantize" method is available.

config/initializers/0_inject_enterprise_edition_module.rb

 # frozen_string_literal: true
+require 'active_support/inflector'
+
 module InjectEnterpriseEditionModule
   def prepend_if_ee(constant)
     prepend(constant.constantize) if Gitlab.ee?

qa/qa.rb

@@ -4,6 +4,9 @@ $: << File.expand_path(File.dirname(__FILE__))
 Encoding.default_external = 'UTF-8'
+require_relative '../lib/gitlab'
+require_relative '../config/initializers/0_inject_enterprise_edition_module'
+
 module QA
   ##
   # GitLab QA runtime classes, mostly singletons.