[IR] Add "Large Data Threshold" module metadata (#66797)

This allows us to not have to pass -mllvm flags to set the large data
threshold for (in-LLD/not-distributed) ThinLTO.

Follows https://reviews.llvm.org/D52322, which did the same for the code
model.

Since the large data threshold is tied to the code model and we disallow
mixing different code models, do the same for the large data threshold.