[sanitizer] Re-introduce kUseSeparateSizeClassForBatch for the 32-bit Primary

Summary:
Currently `TransferBatch` are located within the same memory regions as
"regular" chunks. This is not ideal for security: they make for an interesting
target to overwrite, and are not protected by the frontend (namely, Scudo).

To solve this, we re-introduce `kUseSeparateSizeClassForBatch` for the 32-bit
Primary allowing for `TransferBatch` to end up in their own memory region.
Currently only Scudo would use this new feature, the default behavior remains
unchanged. The separate `kBatchClassID` was used for a brief period of time
previously but removed when the 64-bit ended up using the "free array".

Reviewers: alekseyshl, kcc, eugenis

Reviewed By: alekseyshl

Subscribers: llvm-commits, kubamracek

Differential Revision: https://reviews.llvm.org/D37082

llvm-svn: 311891