[DRAFT] [clang] is_cpp_lambda should only match the call operator of lambdas

[VladimirMakaev]

Procname.is_cpp_lambda matched every method whose name contains operator(), so all function
objects were taken for lambdas: RacerD did not report on them, Pulse suppressed
OPTIONAL_EMPTY_ACCESS in them, and closures passed by value to them lost their captures. Closures
passed to generic lambdas lost them too: the callee got the loaded closure, not its address.

struct CallLambda {
  template <typename F>
  int operator()(F lambda) { return lambda(100); }
};

int capturing_null_through_functor_bad() {
  int* p = nullptr;
  // Infer missed: null dereference
  return CallLambda{}([p](int a) { return a + *p; });
}

is_cpp_lambda now also requires a lambda's closure class, and matches operator() as a prefix
instead of a substring; the new is_cpp_call_operator still matches any operator() for the
std::function model. Closure arguments are now passed by address to every callee, including the
operator() of lambdas.

Test plan

New tests in cpp/pulse, cpp/pulse-17 and cpp/racerd: closures passed to a functor and to a generic
lambda, a closure next to a materialized temporary, optional accesses in a functor and in a struct
declared inside a lambda, and RacerD functors (a lambda_-named class, a template operator(), a
class template). All codetoanalyze cases pass.