[Clang] Fix a crash when taking the address of a consteval lambda

The `_invoke` function of lambdas was not respecting
the constexpr/consteval specifier of the call operator, so it was possible
to take its address in a non-immmediately invoked context,
even if the call operator was itself consteval.

In addition, we improve the diagnostic emmited in the lambda case
not to show that `invoke` method.

Fixes #57682

Reviewed By: aaron.ballman, #clang-language-wg

Differential Revision: https://reviews.llvm.org/D144627