Support new Duplicate operation in Elemental

[Cheddam]

Elemental now has the ability to duplicate blocks. I tested this operation with versioned-snapshots, and found that it did not trigger a snapshot, but that the duplicated blocks would instead be incorporated into the snapshot for the next block that was created normally.

(I'm torn on whether this is a bug or an enhancement - it's a change to support new functionality, but the resulting behaviour without a patch will be buggy 😅)