[clang] [C++20][Modules] Fix crash when function and lambda inside loaded from different modules (PR #109167)

[Dmitry Polukhin via cfe-commits]

dmpolukhin wrote:

I think it is due to this change :( I'm iterating over `Decl*` in `FunctionToLambdasMap`. I'm fixing it by replacing the pointers with LocalDeclID that should be stable.

https://github.com/llvm/llvm-project/pull/109167