alloc zero points consistently

[slumber]

Description

Fix for https://github.com/arkworks-rs/crypto-primitives/pull/115

(0, 1) point is valid affine zero for twisted edwards curve, but this code is for short weierstrass. This causes inconsistency in poseidon sponge usage.

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[slumber]

Note that 23678c645674bb8ea79a2cf2151d89c688257627 should actually be kept, however, it breaks constraints for the on-curve check. I'd suggest to keep it and make Projective::zero() return { 0, 1, 0 }, like it's in-circuit counter part does.

[Pratyush]

@slumber https://github.com/arkworks-rs/r1cs-std/commit/23678c645674bb8ea79a2cf2151d89c688257627 is actually correct, as the coordinates used in the native version are different from the ones used in circuit: the native version uses jacobian coordinates, while the circuit one uses projective ones. The confusing name of SWProjective exacerbates this similarity and leads to confusion.