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

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I'm not sold on this patch, particularly the changes to the overload.  

I also wonder if we would better off having `CXXRecordDecl` save its 'variable' for lambdas (and look it up from there) rather than this.

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