[clang] Don't mark lambda non-dependent if nested in a generic lambda. (PR #149121)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 approved this pull request.

@katzdm 

I apologize for the long delay. After a second thought, I think the patch should work as expected.

Can you please rebase the patch and also add a test case for https://github.com/llvm/llvm-project/issues/156579? The added constant evaluation context reveals another bug, where we considered lambdas non-dependent too eagerly, causing template argument deduction to occur on mismatched template depths.

cc @cor3ntin we should backport this too

https://github.com/llvm/llvm-project/pull/149121