[libclang/python] Refactor enum usage (#95608)

Use Python's builtin enum class instead of writing our own.

This is preparation for passing a strict type check in PR #78114 ,
fixing 927 out of 1341 strict typing errors

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Co-authored-by: Jannick Kremer <jannick-kremer@gmx.de>
Co-authored-by: Vlad Serebrennikov <serebrennikov.vladislav@gmail.com>

Author: DeinAlptraum