fix commit view JS features, reimplement folding (#9968)

* fix commit view JS features, reimplement folding

File content folding was not working so I reimplemented it in a saner
way. Then I noticed the issue was actually because of missing JS
libraries (seen on the console of every commit with error
'SimpleMDE is not defined').

Fixed the libraries. I think the reimplementation is worth to keep.

* add .closest polyfill

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/repo/commit.go

@@ -206,6 +206,8 @@ func FileHistory(ctx *context.Context) {
 func Diff(ctx *context.Context) {
 	ctx.Data["PageIsDiff"] = true
 	ctx.Data["RequireHighlightJS"] = true
+	ctx.Data["RequireSimpleMDE"] = true
+	ctx.Data["RequireTribute"] = true
 
 	userName := ctx.Repo.Owner.Name
 	repoName := ctx.Repo.Repository.Name