gh-113317: Rename libclinic to argclinic

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• Rename Tools/clinic/libclinic/ to Tools/clinic/argclinic/
• Rename Tools/clinic/clinic.py to Tools/clinic/run_argclinic.py.
• Add Tools/clinic/argclinic/main.py.
• Convert absolute imports to imports related to the packages. For example, replace "from libclinic.cli import main" with "from .cli import main".
• Remove "import clinic": import individual names.
• "make clinic" now runs "python -m clinic".

• Issue: Argument Clinic: split out global stateless helpers and constants from clinic.py #113317

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@erlend-aasland: Here is a proposition to replace python clinic.py script with python -m argclinic (add __main__.py).

I also renamed "clinic" to "argclinic" to have a more specific name (be more explicit about the reference to the Monty Python sketch).

The PR is a little bit bigger than expect since there were still a few files importing libclinic to get many functions, rather than importing sub-modules.

[erlend-aasland]

What is the rationale for this change?

[vstinner]

What is the rationale for this change?

My long term goal is to distribute Argument Clinic on PyPI. But I know that you disagree with that. I prefer to close this PR for now.