Add new and delete to DataBlock so it can be used with std::allocator

[lums658]

This PR changes the notion of DataBlock slightly. We now consider the DataBlock to be a single thing that is allocated. According, we no longer consider PoolAllocator as an actual allocator. Rather, we overload new and delete in DataBlockImpl so that DataBlocks can be used directly with std::allocator.

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TYPE: IMPROVEMENT DESC: Add new and delete to DataBlock so it can be used with std::allocator

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #28413: Update interface to PoolAllocator to be completely compliant with standard library requirements.