Lack of confirm before leaving the editing box of Jenkinsfile

Created by: LinuxSuRen

What would you like to be added:

Please see the following screenshot. No matter clicking the Cancel button or type Esc, please make sure don't close the box directly. Or

Why is this needed:

Make sure users can get the confirmation before they leave the editing box of Jenkinsfile. Typing the wrong key is a very normal thing. But it hurts people if they already wrote down many code lines in the editing box. The confirmation is necessary.

/area devops /priority medium