[clang] [clang-tools-extra] [clangd] show lambda name instead of operator() in signature help (PR #101857)

[Timothy Akintilo via cfe-commits]

================
@@ -876,6 +876,11 @@ class Sema;
     /// function pointer or reference (C++ [over.call.object]).
     FunctionDecl *Function;
 
+    /// LambdaName - When the OverloadCandidate is for a
+    /// lambda's operator(), points to the declaration of
+    /// the lambda variable.
+    VarDecl *LambdaName{nullptr};
----------------
tilobyte wrote:

@erichkeane i added tests for immediately-invoked lambdas. could you give an example of a lambda in a template-pack? i was thinking something like 
```
template <typename... Lambda>
auto foo(Lambda... lambda) {
  lambda(^);
}
```
but then the lambda has a name.

https://github.com/llvm/llvm-project/pull/101857