[clang] [Clang] [NFC] Introduce `ConstDynamicRecursiveASTVisitor` (PR #122991)

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Sirraide wrote:

And in the case of `TraverseLambdaCapture` specifically, only 2 parameters need to be `const_cast`, since the `const LambdaCapture *` is already `const` in the RAV implementation.

https://github.com/llvm/llvm-project/pull/122991