Expose diff_refs and full_path for DesignType

https://gitlab.com/gitlab-org/gitlab-ee/issues/9489

ee/app/graphql/types/design_management/design_type.rb

@@ -15,7 +15,9 @@ module Types
       field :project, Types::ProjectType, null: false
       field :issue, Types::IssueType, null: false
       field :filename, GraphQL::STRING_TYPE, null: false
+      field :full_path, GraphQL::STRING_TYPE, null: false
       field :image, GraphQL::STRING_TYPE, null: false, extras: [:parent]
+      field :diff_refs, Types::DiffRefsType, null: false, calls_gitaly: true
       field :versions,
             Types::DesignManagement::VersionType.connection_type,
             resolver: Resolvers::DesignManagement::VersionResolver,

ee/spec/graphql/types/design_management/design_type_spec.rb

@@ -8,7 +8,7 @@ describe GitlabSchema.types['Design'] do
   it { expect(described_class.interfaces).to include(Types::Notes::NoteableType.to_graphql) }
 
   it 'exposes the expected fields' do
-    expected_fields = [:id, :project, :issue, :filename, :image, :versions, :discussions, :notes]
+    expected_fields = [:id, :project, :issue, :filename, :image, :versions, :discussions, :notes, :diff_refs, :full_path]
 
     is_expected.to have_graphql_fields(*expected_fields)
   end