Move distutils command names into package metadata and declare entry points using static config.

[jaraco]

Best practice is to move as much logic out of setup.py and into declarative config. This change achieves that end for entry_points.

Summary of changes

• Move list of commands out of command package and into package metadata.
• Materialize the distutils.commands.
• Move entry points to declarative config.

Pull Request Checklist

• News fragment added in changelog.d/.
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