Support faster, leaky shutdown

[bliptec]

For Edge, OneDS (if it's started) will live for as long as the browser, so it'll only ever get shut down right before the process exits. There's no reason to clean up resources (join threads, de-allocate memory, etc) that the OS is about to reclaim anyways. The only things that need to happen are:

1. Persistent storage has all the latest data reasonably flushed
2. Threads and callbacks are in a state where they won't behave poorly (ie. potentially cause access violations) as everything shuts down. Could be achieved by a combination of relying on weak pointers and ensuring pending work finishes.