[clang] [clang][modules] Separate parsing of modulemaps (PR #119740)

[Ben Langmuir via cfe-commits]

https://github.com/benlangmuir commented:

I'm happy with the way this split of the code worked out!

> Currently this has no effect other than slightly changing diagnostics.

Can you say more about the ordering changes? I understand we can't always emit diagnostics in source order, but it's helpful for readability when we do so I wasn't thrilled to see that seems to be changing.

https://github.com/llvm/llvm-project/pull/119740