Remove WorkingCopyBaseService

The working copy for squash and rebases, among other git operations, has
been a concern of Gitaly for a long time. This service is an old
artifact of the time GitLab-Rails was responsible for it.

This service contains little code, and the code it did contain I've
moved to the usual base service.

Closes: https://gitlab.com/gitlab-org/gitlab/issues/36067

app/services/merge_requests/working_copy_base_service.rb → app/services/concerns/git/logger.rb

 # frozen_string_literal: true
 
-module MergeRequests
-  class WorkingCopyBaseService < MergeRequests::BaseService
-    attr_reader :merge_request
-
-    def source_project
-      @source_project ||= merge_request.source_project
-    end
-
-    def target_project
-      @target_project ||= merge_request.target_project
-    end
-
+module Git
+  module Logger
     def log_error(message, save_message_on_model: false)
       Gitlab::GitLogger.error("#{self.class.name} error (#{merge_request.to_reference(full: true)}): #{message}")
-
       merge_request.update(merge_error: message) if save_message_on_model
     end
-
-    # Don't try to print expensive instance variables.
-    def inspect
-      "#<#{self.class} #{merge_request.to_reference(full: true)}>"
-    end
   end
 end

app/services/merge_requests/base_service.rb

@@ -29,6 +29,19 @@ module MergeRequests
                                  .execute_for_merge_request(merge_request)
     end
 
+    def source_project
+      @source_project ||= merge_request.source_project
+    end
+
+    def target_project
+      @target_project ||= merge_request.target_project
+    end
+
+    # Don't try to print expensive instance variables.
+    def inspect
+      "#<#{self.class} #{merge_request.to_reference(full: true)}>"
+    end
+
     private
 
     def create(merge_request)

app/services/merge_requests/rebase_service.rb

 # frozen_string_literal: true
 
 module MergeRequests
-  class RebaseService < MergeRequests::WorkingCopyBaseService
+  class RebaseService < MergeRequests::BaseService
+    include Git::Logger
+
     REBASE_ERROR = 'Rebase failed. Please rebase locally'
 
+    attr_reader :merge_request
+
     def execute(merge_request)
       @merge_request = merge_request
 

app/services/merge_requests/squash_service.rb

 # frozen_string_literal: true
 
 module MergeRequests
-  class SquashService < MergeRequests::WorkingCopyBaseService
+  class SquashService < MergeRequests::BaseService
+    include Git::Logger
+
     def execute
       # If performing a squash would result in no change, then
       # immediately return a success message without performing a squash