[Notif] Write AppUid earlier in NotificationInfo

Noticed that appuid was being used but it wasn't set until later in the
lifecycle of the notificationinfo (rendering the channel logic moot).

If the notif is now posting notificiations to the default channel while
having multiple channels, it'll now show "Uncategorized" in the blocking
helper/notification info screens.

Fixes: 77240828
Test: Ran NotifInfoTest (added one new test case)
Test: Visually, artificially sent default ch notif with app having 9 ch
Change-Id: I45f2c35fb6dae610e511b2d316b3c184b84f2d09