Wrap deface overrides in a module and add relation type menu

Zeitwerk expects a class or module correctly named in these files.
We can simply create the expected named modules to appease Zeitwerk.

Add relation type in backend menu using initializer.

Author: JustShah

app/overrides/add_product_relation_admin_sub_menu_tab.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module SolidusRelatedProduct
+  module AddRelatedProductAdminTabs
+    Deface::Override.new(
+      virtual_path: 'spree/admin/shared/_product_tabs',
+      name: 'add_related_products_admin_tab',
+      insert_bottom: '[data-hook="admin_product_tabs"]',
+      partial: 'spree/admin/products/related_products',
+      original: '4baaf4bff6bb1ddf0a8f9592833bd5794a3b1943'
+    )
+  end
+end

app/overrides/add_related_product_admin_tabs.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module SolidusRelatedProduct
+  module AddRelatedProductsToVariant
+    Deface::Override.new(
+      virtual_path: 'spree/admin/variants/edit',
+      name: 'add_related_products_to_variant',
+      insert_before: "erb[loud]:contains('form_for')",
+      partial: 'spree/admin/variants/related'
+    )
+  end
+end

app/overrides/add_related_products_to_variant.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+Rails.application.config.to_prepare do
+  Spree::Backend::Config.configure do |config|
+    config.menu_items = config.menu_items.map do |item|
+      if item.label.to_sym == :products
+        # The API of the MenuItem class changes in Solidus 4.2.0
+        if item.respond_to?(:children)
+          unless item.children.any? { |child| child.label == :relation_types }
+            item.children << Spree::BackendConfiguration::MenuItem.new(
+              label: :relation_types,
+              condition: -> { can?(:admin, Spree::RelationType) },
+              url: -> { Spree::Core::Engine.routes.url_helpers.admin_relation_types_path },
+              match_path: "/relation_types"
+            )
+          end
+        else
+          item.sections << :relation_types
+        end
+      end
+      item
+    end
+  end
+end