Apply Rails standard to base mailer class

It has the advantage that `rails generate mailer` works out of the box
and we comply with rubocop rules.

.rubocop_todo.yml

@@ -810,12 +810,6 @@ Rails/ApplicationJob:
   Exclude:
     - 'app/jobs/report_job.rb'
 
-# Offense count: 1
-# This cop supports unsafe autocorrection (--autocorrect-all).
-Rails/ApplicationMailer:
-  Exclude:
-    - 'app/mailers/spree/base_mailer.rb'
-
 # Offense count: 5
 # This cop supports unsafe autocorrection (--autocorrect-all).
 # Configuration parameters: NilOrEmpty, NotPresent, UnlessPresent.

app/mailers/application_mailer.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class ApplicationMailer < ActionMailer::Base
+  # Inline stylesheets
+  include Roadie::Rails::Automatic
+
+  helper TermsAndConditionsHelper
+
+  default from: -> { Spree::Config[:mails_from] }
+  layout 'mailer'
+
+  def money(amount)
+    Spree::Money.new(amount).to_s
+  end
+  helper_method :money
+
+  protected
+
+  def roadie_options
+    # This lets us specify assets using relative paths in email templates
+    super.merge(url_options: { host: URI(main_app.root_url).host })
+  end
+end

app/mailers/enterprise_mailer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 require 'devise/mailers/helpers'
-class EnterpriseMailer < Spree::BaseMailer
+class EnterpriseMailer < ApplicationMailer
   include Devise::Mailers::Helpers
   include I18nHelper
 

app/mailers/payment_mailer.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class PaymentMailer < Spree::BaseMailer
+class PaymentMailer < ApplicationMailer
   include I18nHelper
 
   def authorize_payment(payment)

app/mailers/producer_mailer.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class ProducerMailer < Spree::BaseMailer
+class ProducerMailer < ApplicationMailer
   include I18nHelper
 
   def order_cycle_report(producer, order_cycle)

app/mailers/spree/base_mailer.rb

@@ -1,25 +0,0 @@
-# frozen_string_literal: true
-
-module Spree
-  class BaseMailer < ActionMailer::Base
-    # Inline stylesheets
-    include Roadie::Rails::Automatic
-
-    helper TermsAndConditionsHelper
-
-    default from: -> { Spree::Config[:mails_from] }
-    layout 'mailer'
-
-    def money(amount)
-      Spree::Money.new(amount).to_s
-    end
-    helper_method :money
-
-    protected
-
-    def roadie_options
-      # This lets us specify assets using relative paths in email templates
-      super.merge(url_options: { host: URI(main_app.root_url).host })
-    end
-  end
-end

app/mailers/spree/order_mailer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module Spree
-  class OrderMailer < BaseMailer
+  class OrderMailer < ApplicationMailer
     helper 'checkout'
     helper SpreeCurrencyHelper
     helper Spree::PaymentMethodsHelper

app/mailers/spree/shipment_mailer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module Spree
-  class ShipmentMailer < BaseMailer
+  class ShipmentMailer < ApplicationMailer
     def shipped_email(shipment, delivery:)
       @shipment = shipment.respond_to?(:id) ? shipment : Spree::Shipment.find(shipment)
       @delivery = delivery

app/mailers/spree/test_mailer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module Spree
-  class TestMailer < BaseMailer
+  class TestMailer < ApplicationMailer
     def test_email(user)
       recipient = user.respond_to?(:id) ? user : Spree::User.find(user)
       subject = "#{Spree::Config[:site_name]} #{t('spree.test_mailer.test_email.subject')}"

app/mailers/spree/user_mailer.rb

@@ -3,7 +3,7 @@
 # This mailer is configured to be the Devise mailer
 # Some methods here override Devise::Mailer methods
 module Spree
-  class UserMailer < BaseMailer
+  class UserMailer < ApplicationMailer
     include I18nHelper
 
     helper MailerHelper

app/mailers/subscription_mailer.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class SubscriptionMailer < Spree::BaseMailer
+class SubscriptionMailer < ApplicationMailer
   helper 'checkout'
   helper MailerHelper
   helper ShopMailHelper