[clang] [Clang] [NFC] Introduce `ConstDynamicRecursiveASTVisitor` (reland) (PR #124821)

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Sirraide wrote:

> I don't think `.template` is incorrect. Maybe you hit #96364 or somethink @sdkrystian

Yeah, at first I thought it was required, apparently it’s not. GCC and Clang accept both, but I also don’t think it’s incorrect, so... I’m still somewhat confused about this

https://github.com/llvm/llvm-project/pull/124821