errors: Misc improvements

* Redo the server error template
* Always add the content file context if relevant
* Remove some now superflous error string matching
* Move the server error template to _server/error.html
* Add file context (with position) to codeblock render blocks
* Improve JS build errors

Fixes #9892
Fixes #9891
Fixes #9893

tpl/tplimpl/template_errors.go

@@ -59,6 +59,6 @@ func (info templateInfo) errWithFileContext(what string, err error) error {
 		return err
 	}
 	defer f.Close()
-	return fe.UpdateContent(f, herrors.SimpleLineMatcher)
+	return fe.UpdateContent(f, nil)
 
 }