[clang] [Serialization] Fix lazy template loading (PR #133057)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> Except that it will make using the stl and related modules _much_ faster which is a significant quality of life improvement imo.
> 
> EDIT: And make the clang peak memory when using modules lower :)

Of course, this is why we want this. But for releases, I don't think we should take the risk for the actually NFC change.

https://github.com/llvm/llvm-project/pull/133057