[clang] [llvm] [SROA] Refactor rewritePartition alloca type selection process (PR #167771)

[Yonah Goldberg via llvm-commits]

YonahGoldberg wrote:

Going to merge this tomorrow. Giving advance notice for the other people I pinged in case they want to review.

https://github.com/llvm/llvm-project/pull/167771