Allows a page to show popups during its unloading (obsolete)

OBSOLETE: This policy is obsolete and doesn't work after Microsoft Edge 87. This policy allows an admin to specify that a page can show popups during its unloading. When the policy is set to enabled, pages are allowed to show popups while they're being unloaded. When the policy is set to disabled or unset, pages aren't allowed to show popups while they're being unloaded. This restriction is as per the spec: (https://html.spec.whatwg.org/#apis-for-creating-and-navigating-browsing-contexts-by-name). This policy was removed in Microsoft Edge 88 and is ignored if set.