Make Gitlab::GlRepository#types an instance method

Having this as an instance method makes it easier to override in the
prepended `EE` module.

If we try to override this method on the module itself, it would not
be overridden correctly, depending on the load order.

ee/lib/ee/gitlab/gl_repository.rb

@@ -3,6 +3,7 @@
 module EE
   module Gitlab
     module GlRepository
+      extend ::Gitlab::Utils::Override
       extend ActiveSupport::Concern
 
       DESIGN = ::Gitlab::GlRepository::RepoType.new(
@@ -15,11 +16,10 @@ module EE
         DESIGN.name.to_s => DESIGN
       }.freeze
 
-      class_methods do
+      override :types
       def types
         super.merge(EE_TYPES)
       end
     end
   end
-  end
 end

ee/spec/lib/gitlab/gl_repository_spec.rb

@@ -9,4 +9,12 @@ describe Gitlab::GlRepository do
       expect(described_class.parse("design-#{project.id}")).to eq([project, EE::Gitlab::GlRepository::DESIGN])
     end
   end
+
+  describe '.types' do
+    it 'contains both the EE and CE repository types' do
+      expected_types = Gitlab::GlRepository::TYPES.merge(EE::Gitlab::GlRepository::EE_TYPES)
+
+      expect(described_class.types).to eq(expected_types)
+    end
+  end
 end

lib/gitlab/gl_repository.rb

 # frozen_string_literal: true
 
 module Gitlab
-  module GlRepository
+  class GlRepository
+    include Singleton
+
     PROJECT = RepoType.new(
       name: :project,
       access_checker_class: Gitlab::GitAccess,
@@ -19,7 +21,7 @@ module Gitlab
     }.freeze
 
     def self.types
-      TYPES
+      instance.types
     end
 
     def self.parse(gl_repository)
@@ -39,7 +41,13 @@ module Gitlab
     def self.default_type
       PROJECT
     end
+
+    def types
+      TYPES
+    end
+
+    private_class_method :instance
   end
 end
 
-::Gitlab::GlRepository.prepend(::EE::Gitlab::GlRepository)
+Gitlab::GlRepository.prepend(::EE::Gitlab::GlRepository)

lib/gitlab/gl_repository/repo_type.rb

 # frozen_string_literal: true
 
 module Gitlab
-  module GlRepository
+  class GlRepository
     class RepoType
       attr_reader :name,
                   :access_checker_class,