Replace jquery.confirmExit

[onEXHovia]

Subject

Parts #7158 #7156

Changelog

### Changed
Replace jquery.confirmExit to vanilla js

[VincentLanglet]

Isn't a code-smell to have a non consistent return ?

What should be fore if this.snapshotValue === this.snapshot ?

[onEXHovia]

return '' or return null or return false it may trigger dialog, of course if use retrun; will be work but eslint all the same throw error. We are already disable rule in https://github.com/sonata-project/SonataAdminBundle/blob/4.x/assets/js/jquery.confirmExit.js#L20

[onEXHovia]

Im mean it's will be not work, eslint all the same throw consistent-return error

  beforeUnload(event) {
    const message = Translation.trans('CONFIRM_EXIT');
    if (this.snapshotValue === this.snapshot) {
      return;
    }

    event.returnValue = message;
    return message;
  }

[jordisala1991]

Consider adding tests to this new controllers. It should be way easy to test this features with stimulus