gh-113317: Argument Clinic: Add libclinic.clanguage

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Add libclinic.lang_c module and move the following classes and functions there:

• CLanguage
• declare_parser()

Add libclinic.codegen and move the following classes there:

• BlockPrinter
• BufferSeries
• Destination

Move these functions to libclinic.function:

• permute_left_option_groups()
• permute_optional_groups()
• permute_right_option_groups()

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

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@erlend-aasland: I updated the PR to address your review. Please review the updated PR.

I used git rebase to rewrite the commit message and rename files.

[erlend-aasland]

Thanks! I think libclinic.codegen makes sense. Also, it makes sense to put the option group stuff together with the parameter stuff (currently in function.py).

I realise that we already got a libclinic.language.py file with the PythonLanguage and Language classes. I'm fine with using clanguage.py instead of lang_c.py, as was your original suggestion. Up to you.

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I realise that we already got a libclinic.language.py file with the PythonLanguage and Language classes. I'm fine with using clanguage.py instead of lang_c.py, as was your original suggestion. Up to you.

I renamed the file to clanguage.py.