[clang] Ast importer visitors (PR #138838)

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ganenkokb-yandex wrote:

> I think we can put in this change. I tested it on some projects, the number of crashes got less after this change (it is possible that new ones appeared but the total count was less).

Thank you for your attention.
What additional steps are expected of me to take the pull request further?

https://github.com/llvm/llvm-project/pull/138838