Stores normalized version constraints in the lockfile, which will
improve reproducibility and will fix a bug with duplicate specifiers
ending up in the lockfile. Also, gets rid of some duplicate data in the
specifiers area of the lockfile.
Closes #18296.
Adds a `--frozen` (alias `--frozen-lockfile`) flag that errors out if
the lockfile is out of date. This is useful for running in CI (where an
out of date lockfile is usually a mistake) or to prevent accidental
changes in dependencies.
