[TASK] Update VAnchor to use new SetGadget

[lazovicff]

VAnchor is using the old SetMembershipGadget that requires computing the diffs outside the circuit and passing them in. This means that you need to know the root beforehand, which is not an ideal way of making proofs. The root will be calculated inside the circuit, based on provided leaf pre-image and Merkle path, so the diffs will also be calculated inside the circuit.