main packages usually go under a `cmd` directory.
Hoist utility packages to the root `src` directroy so they can be shared.
Change-Id: I0c221f6cd39980f5c202c030cd5134d775533efa
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50901
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>
Ben Clayton