[clang] [WIP] [Modules] Delay reading type source info of the preferred_name attribute. (PR #122250)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

I have jumped ahead of the train and left some comments. Feel free to ignore them for now, I'd be happy to do another round of review when it's actually ready.

https://github.com/llvm/llvm-project/pull/122250