Add a top-level project structure test to reject new package-lock files

[johndayrichter]

Because checkins to this repo require dependency hoisting, the introduction of a new package-lock file is always evidence of a problem. A new package-lock file means that two packages in this monorepo require different versions of the same dependency.

We should introduce a top-level project-structure test that enforces invariants on the repo like this one, and fails if a subproject is out of compliance.