We reuse the prev_name allocation for Entry, instead of allocating and
returning a separate Vec.
We encode the `prev_name: None` case as an empty vector, since we don't
allow empty names anyway, and the sorting is equivalent.
Change-Id: I975b37ff873805f5ff099bc82128706891052247
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11607
Reviewed-by: Brian Olsen <me@griff.name>
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
31d73cd443