[clang] [RFC][C++20][Modules] Fix crash when function and lambda inside loaded from different modules (PR #104512)

[Dmitry Polukhin via cfe-commits]

dmpolukhin wrote:

@ChuanqiXu9  please take another look. I changed approach to remember which lambdas exist in FunctionDecl and load them for the first decl. I'm still testing it but interested to know does it look like something that address your concernes?

https://github.com/llvm/llvm-project/pull/104512