feat(diff): Enable commenting on expanded lines in PR diffs (#35662)

Fixes #32257 
/claim #32257

Implemented commenting on unchanged lines in Pull Request diffs, lines
are accessed by expanding the diff preview. Comments also appear in the
"Files Changed" tab on the unchanged lines where they were placed.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/pull.go

@@ -827,6 +827,12 @@ func viewPullFiles(ctx *context.Context, beforeCommitID, afterCommitID string) {
 	}
 
 	ctx.Data["Diff"] = diff
+	ctx.Data["DiffBlobExcerptData"] = &gitdiff.DiffBlobExcerptData{
+		BaseLink:       ctx.Repo.RepoLink + "/blob_excerpt",
+		PullIssueIndex: pull.Index,
+		DiffStyle:      ctx.FormString("style"),
+		AfterCommitID:  afterCommitID,
+	}
 	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
 	if ctx.IsSigned && ctx.Doer != nil {