[clang] [Clang] [CodeGen] Perform derived-to-base conversion on explicit object parameter in lambda (PR #89828)

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cor3ntin wrote:

You should run make_cxx_drs, otherwise I think this looks in good shape.

I think we should diag earlier (because if the lambda is not use we should still signal it's broken) but doing that as a follow up PR seems reasonable.

Less redundant diags is better but if we can't avoid it, i think it's a reasonable compromise

https://github.com/llvm/llvm-project/pull/89828