Adopt setuptools_scm

[jaraco]

• Replace static version with setuptools-scm version.
• Remove bumpversion and rely on jaraco.develop for finalize operation.
• Vendor setuptools_scm instead of declaring it to avoid bootstrapping issue.

Summary of changes

Closes #4530

Pull Request Checklist

• [x] Changes have tests
• [x] News fragment added in newsfragments/. (See documentation for details)

[jaraco]

I don't understand the test failures. The tests pass for me locally. Also, the test failures seem largely unrelated to the change. The only thing I can think is that maybe the tests are somehow reliant on Setuptools' own MANIFEST.in. I'm going to sleep on it and tomorrow try to replicate the issue in a Docker image or using the act tool.