Prepare for separation of RSpec helper files

Since rspec-rails 3, the default installation creates two helper files:
* `spec_helper.rb`
* `rails_helper.rb`

`spec_helper.rb` is intended as a way of running specs that do not
require Rails, whereas `rails_helper.rb` loads Rails (as Discourse's
current `spec_helper.rb` does).

For more information:

https://www.relishapp.com/rspec/rspec-rails/docs/upgrade#default-helper-files

In this commit, I've simply replaced all instances of `spec_helper` with
`rails_helper`, and renamed the original `spec_helper.rb`.

This brings the Discourse project closer to the standard usage of RSpec
in a Rails app.

At present, every spec relies on loading Rails, but there are likely
many that don't need to. In a future pull request, I hope to introduce a
separate, minimal `spec_helper.rb` which can be used in tests which
don't rely on Rails.

spec/components/validators/allowed_ip_address_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe AllowedIpAddressValidator do
 

spec/components/validators/email_setting_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe EmailSettingValidator do
   describe '#valid_value?' do

spec/components/validators/email_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe EmailValidator do
 

spec/components/validators/integer_setting_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe IntegerSettingValidator do
   describe '#valid_value?' do

spec/components/validators/ip_address_format_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe IpAddressFormatValidator do
 

spec/components/validators/password_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 require_dependency "common_passwords/common_passwords"
 
 describe PasswordValidator do

spec/components/validators/post_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 require_dependency 'validators/post_validator'
 
 describe Validators::PostValidator do

spec/components/validators/quality_title_validator_spec.rb

@@ -1,6 +1,6 @@
 # encoding: UTF-8
 
-require 'spec_helper'
+require 'rails_helper'
 require 'validators/quality_title_validator'
 require 'ostruct'
 

spec/components/validators/reply_by_email_address_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe ReplyByEmailAddressValidator do
 

spec/components/validators/string_setting_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe StringSettingValidator do
 

spec/components/validators/topic_title_length_validator_spec.rb

@@ -1,6 +1,6 @@
 # encoding: UTF-8
 
-require 'spec_helper'
+require 'rails_helper'
 require 'validators/topic_title_length_validator'
 
 describe TopicTitleLengthValidator do

spec/components/validators/user_full_name_validator_spec.rb

@@ -1,4 +1,4 @@
-require "spec_helper"
+require "rails_helper"
 
 describe UserFullNameValidator do
   let(:validator) { described_class.new({attributes: :name}) }

spec/components/validators/username_setting_validator_spec.rb

@@ -1,4 +1,4 @@
-require 'spec_helper'
+require 'rails_helper'
 
 describe UsernameSettingValidator do
   describe '#valid_value?' do