Create a tool to manage version requirements in manifest and lock files

[ia0]

We want the following properties:

• Lock files match manifest files. If a direct dependency version requirement is M.m.p, then the lock file should use M.m.p. This means that if some crate in the dependency tree has a stronger requirement, then the manifest must be updated to reflect that.
• Lock files should use the minimal version of indirect dependencies. The goal is to test that all possible dependency version resolutions compile. (Note that this assumes semver. If a dependency breaks semver, it should ideally be fixed and yanked, restoring semver at crates.io level.)
• When upgrading all dependencies, only direct dependencies for which a new major version has been published must be updated. The chosen version requirement should be minimal.
• We rely on dependabot and cargo audit to figure out if a version is vulnerable and should be bumped (usually patch version).
• Direct dependency versions may also be bumped if a specific feature of a minor version is needed.
• For crates that build on stable and the guarantee that they build on stable, we should provide package.rust-version and somehow check it (probably run test.sh with the MSRV too)

See rust-lang/cargo#14372 for more information.