Refactor cycle analytics summary base classes

Refactor to avoid multiple identical definitions of `links`, `identifier`,
`title` and `value`.

ee/lib/gitlab/analytics/cycle_analytics/summary/base_time.rb

@@ -5,6 +5,8 @@ module Gitlab
     module CycleAnalytics
       module Summary
         class BaseTime
+          include Gitlab::CycleAnalytics::Summary::Defaults
+
           def initialize(stage:, current_user:, options:)
             @stage = stage
             @current_user = current_user
@@ -13,10 +15,6 @@ module Gitlab
             assign_stage_metadata
           end
 
-          def identifier
-            self.class.name.demodulize.underscore.to_sym
-          end
-
           def value
             @value ||= Gitlab::CycleAnalytics::Summary::Value::PrettyNumeric.new(data_collector.median.days&.round(1))
           end
@@ -33,10 +31,6 @@ module Gitlab
             raise NotImplementedError, "Expected #{self.name} to implement end_event_identifier"
           end
 
-          def links
-            []
-          end
-
           private
 
           # rubocop: disable CodeReuse/ActiveRecord

ee/lib/gitlab/analytics/cycle_analytics/summary/group/base.rb

@@ -6,28 +6,14 @@ module Gitlab
       module Summary
         module Group
           class Base
+            include Gitlab::CycleAnalytics::Summary::Defaults
+
             attr_reader :group, :options
 
             def initialize(group:, options:)
               @group = group
               @options = options
             end
-
-            def identifier
-              self.class.name.demodulize.underscore.to_sym
-            end
-
-            def title
-              raise NotImplementedError, "Expected #{self.name} to implement title"
-            end
-
-            def value
-              raise NotImplementedError, "Expected #{self.name} to implement value"
-            end
-
-            def links
-              []
-            end
           end
         end
       end

ee/lib/gitlab/analytics/cycle_analytics/summary/lead_time_for_changes.rb

@@ -25,10 +25,6 @@ module Gitlab
             n_('day', 'days', value)
           end
 
-          def links
-            []
-          end
-
           private
 
           attr_reader :stage, :current_user, :options, :from, :to

lib/gitlab/cycle_analytics/summary/base.rb

@@ -4,27 +4,13 @@ module Gitlab
   module CycleAnalytics
     module Summary
       class Base
+        include Gitlab::CycleAnalytics::Summary::Defaults
+
         def initialize(project:, options:)
           @project = project
           @options = options
         end
 
-        def identifier
-          self.class.name.demodulize.underscore.to_sym
-        end
-
-        def title
-          raise NotImplementedError, "Expected #{self.name} to implement title"
-        end
-
-        def value
-          raise NotImplementedError, "Expected #{self.name} to implement value"
-        end
-
-        def links
-          []
-        end
-
         private
 
         attr_reader :project, :options

lib/gitlab/cycle_analytics/summary/defaults.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module CycleAnalytics
+    module Summary
+      module Defaults
+        def identifier
+          self.class.name.demodulize.underscore.to_sym
+        end
+
+        # :nocov: the class including this concern is expected to test this method.
+        def title
+          raise NotImplementedError, "Expected #{self.name} to implement title"
+        end
+        # :nocov:
+
+        # :nocov: the class including this concern is expected to test this method.
+        def value
+          raise NotImplementedError, "Expected #{self.name} to implement value"
+        end
+        # :nocov:
+
+        def links
+          []
+        end
+      end
+    end
+  end
+end