Place inline diff comment dialogs on split diff in 4th and 8th columns (#18403) (#18404)

Backport #18403

Fix #18391
Fix #18320

Signed-off-by: Andrew Thornton <art27@cantab.net>

web_src/js/features/repo-issue.js

@@ -496,9 +496,11 @@ export function initRepoPullRequestReview() {
         <tr class="add-comment" data-line-type="${lineType}">
           ${isSplit ? `
             <td class="lines-num"></td>
+            <td class="lines-escape"></td>
             <td class="lines-type-marker"></td>
             <td class="add-comment-left"></td>
             <td class="lines-num"></td>
+            <td class="lines-escape"></td>
             <td class="lines-type-marker"></td>
             <td class="add-comment-right"></td>
           ` : `