Snapshot RemoteViews before releasing lock.

The MSG_NOTIFY_UPDATE_APP_WIDGET message is sent asynchronously,
meaning it tries sending RemoteViews without the lock held, possibly
while another Binder thread is trying to mutate it.

Fix this by creating a copy for the thread to safely dispatch.

Bug: 29889779
Change-Id: I341fbbf89abee97a66cd67f1dd2a728282b68bfa