Use new and old paths instead of just the new path for diff batching

Issue: gitlab.com/gitlab-org/gitlab/-/issues/334273
MR: gitlab.com/gitlab-org/gitlab/-/merge_requests/66873

Changelog: fixed

app/models/merge_request_diff.rb

@@ -395,10 +395,10 @@ class MergeRequestDiff < ApplicationRecord
       if comparison
         if diff_options[:paths].blank? && !without_files?
           # Return the empty MergeRequestDiffBatch for an out of bound batch request
-          break diffs_batch if diffs_batch.diff_file_paths.blank?
+          break diffs_batch if diffs_batch.diff_paths.blank?
 
           diff_options.merge!(
-            paths: diffs_batch.diff_file_paths,
+            paths: diffs_batch.diff_paths,
             pagination_data: diffs_batch.pagination_data
           )
         end

lib/gitlab/diff/file_collection/base.rb

@@ -43,10 +43,16 @@ module Gitlab
           end
         end
 
+        # This is either the new path, otherwise the old path for the diff_file
         def diff_file_paths
           diff_files.map(&:file_path)
         end
 
+        # This is both the new and old paths for the diff_file
+        def diff_paths
+          diff_files.map(&:paths).flatten.uniq
+        end
+
         def pagination_data
           @pagination_data || empty_pagination_data
         end

spec/models/merge_request_diff_spec.rb

@@ -465,11 +465,13 @@ RSpec.describe MergeRequestDiff do
         it 'sorts diff files directory first' do
           diff_with_commits.update!(sorted: false) # Mark as unsorted so it'll re-order
 
-          expect(diff_with_commits.diffs_in_batch(0, 10, diff_options: diff_options).diff_file_paths).to eq([
+          # There will be 11 returned, as we have to take into account for new and old paths
+          expect(diff_with_commits.diffs_in_batch(0, 10, diff_options: diff_options).diff_paths).to eq([
             'bar/branch-test.txt',
             'custom-highlighting/test.gitlab-custom',
             'encoding/iso8859.txt',
             'files/images/wm.svg',
+            'files/js/commit.js.coffee',
             'files/js/commit.coffee',
             'files/lfs/lfs_object.iso',
             'files/ruby/popen.rb',
@@ -553,11 +555,12 @@ RSpec.describe MergeRequestDiff do
         it 'sorts diff files directory first' do
           diff_with_commits.update!(sorted: false) # Mark as unsorted so it'll re-order
 
-          expect(diff_with_commits.diffs(diff_options).diff_file_paths).to eq([
+          expect(diff_with_commits.diffs(diff_options).diff_paths).to eq([
             'bar/branch-test.txt',
             'custom-highlighting/test.gitlab-custom',
             'encoding/iso8859.txt',
             'files/images/wm.svg',
+            'files/js/commit.js.coffee',
             'files/js/commit.coffee',
             'files/lfs/lfs_object.iso',
             'files/ruby/popen.rb',