Add CurrentURL template variable back (#37444)

Because some custom template users need it, also add a new test and
comments

services/context/context.go

@@ -163,6 +163,7 @@ func Contexter() func(next http.Handler) http.Handler {
 			base := NewBaseContext(resp, req)
 			ctx := NewWebContext(base, rnd, session.GetContextSession(req))
 			ctx.Data.MergeFrom(middleware.CommonTemplateContextData())
+			ctx.Data["CurrentURL"] = setting.AppSubURL + req.URL.RequestURI()
 			ctx.Data["Link"] = ctx.Link
 
 			// PageData is passed by reference, and it will be rendered to `window.config.pageData` in `head.tmpl` for JavaScript modules