[NFC][SROA] Clean up rewritePartition type selection process#169106

AlexMaclean merged 3 commits intollvm:mainllvm/llvm-project:mainfrom

YonahGoldberg:yonah/rewrite-partition-small-cleanupYonahGoldberg/llvm-project:yonah/rewrite-partition-small-cleanupCopy head branch name to clipboard