[clang] [Clang][Sema] Properly get captured 'this' pointer in lambdas with an explicit object parameter in constant evaluator (PR #81102)

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Sirraide wrote:

CC @AaronBallman, @cor3ntin, @shafik, @erichkeane, @Endilll 

https://github.com/llvm/llvm-project/pull/81102