Closes NotificationRankingUpdate fd after write

Adds close and unmap buffer to NotificationRankingUpdate writeToParcel.
This should be safe to do (and good to prevent memory leaks) because
there's a per-process counter on the SharedMemory fd, and the
NotificationListeners who will receive this update have the pointer, so
the memory shouldn't actually be cleared.

Test: atest NotificationRankingUpdateTest, atest SystemUIMicrobenchmark:android.platform.test.scenario.notification.PostAndClearNotificationMicrobenchmark
Bug: 308308726
Change-Id: I70a5d31d0969cc82ef5462865ad035093c757017