Add support for rearranging tracks from the UI

Maybe there is a way to do this but I couldn't find it. In my head I would expect there to be a grab handle somewhere on the process/thread list and that would let me move things to a new order.

Start by locating the Perfetto UI component that renders the process/thread list and inspect how its current order is represented. The work is done when the UI exposes a grab handle and users can move tracks into a new order.

Written by the indexing model from the issue text.