[clang] [clang][DependencyScanning] Track dependencies from prebuilt modules to determine IsInStableDir (PR #132237)

[Cyndy Ishida via cfe-commits]

cyndyishida wrote:

>From the previous PR: 

> This implementation adds some overhead for two reasons.
>
> It deserializes out more content from prebuilt pcm files.
> When a module path is fully realized, it traverses down into the leaf dependency and updates whether they are in the sysroot.
> I measured this overhead on a large-ish objc project that uses pch's and toy examples against the macos sdk. I did not observe a noticeable difference.

https://github.com/llvm/llvm-project/pull/132237