Show outdated comments in files changed tab (#24936)

If enabled show a clickable label in the comment. A click on the label
opens the Conversation tab with the comment focussed - there you're able
to view the old diff (or original diff the comment was created on).

**Screenshots**


![image](63ab9571-a9ee-4900-9f02-94ab0095f9e7)

![image](78f7c225-8d76-46f5-acfd-9b8aab988a6c)



When resolved and outdated:

![image](6ece9ebd-c792-4aa5-9c35-628694e9d093)

Option to enable/disable this (stored in user settings - default is
disabled):

![image](ed99dfe4-76dc-4c12-bd96-e7e62da50ab5)

![image](e837a052-e92e-4a28-906d-9db5bacf93a6)



fixes #24913

---------

Co-authored-by: silverwind <me@silverwind.io>

routers/web/repo/pull.go

@@ -761,7 +761,7 @@ func ViewPullFiles(ctx *context.Context) {
 		"numberOfViewedFiles": diff.NumViewedFiles,
 	}
 
-	if err = diff.LoadComments(ctx, issue, ctx.Doer); err != nil {
+	if err = diff.LoadComments(ctx, issue, ctx.Doer, ctx.Data["ShowOutdatedComments"].(bool)); err != nil {
 		ctx.ServerError("LoadComments", err)
 		return
 	}