[Foundation] Migrate Data to a ABI stable variant

This has one known performance regression; appending with a sequence (not an Array, but something like a Repeated<UInt8>) is slower. We aknowlege this regression and plan to offer an update later that has a specialized variation of this API that optimizes to a memset/memset_pattern. This set of changes is limited to specifically targeting ABI stability and inline characteristics of Data and leaves that optimization as a future addition.

Author: phausler