Use FCMP implementation of BP+ in monero-serai (#344)

* Add in an implementation of BP+ based off the paper, intended for clarity and review

This was done as part of my work on FCMPs from Monero, and is copied from https://github.com/kayabaNerve/full-chain-membership-proofs

* Remove crate structure of BP+

* Remove arithmetic circuit code

* Remove AC/VC generators code

* Remove generator transcript

Monero uses non-transcripted static generators.

* Further trimming of generators

* Remove the single range proof

It's unused by Monero and accordingly unhelpful.

* Work on getting BP+ to compile in its new env

* Correct BP+ folder name

* Further tweaks to get closer to compiling

* Remove the ScalarMatrix file

It's only used for AC proofs

* Compiles, with tests passing

* Lock BP+ to Ed25519 instead of the generic Ciphersuite

* Resolve most warnings in BP+

* Make existing bulletproofs test easier to read

* Further strip generators

* Swap G/H as Monero did

* Replace RangeCommitment with Commitment

* Hard-code BP+ h to Ed25519's generator

* Use pub(crate) for BP+, not pub

* Replace initial_transcript with hash_plus

* Rename hash_plus to initial_transcript

* Finish integrating the FCMP BP+ impl

* Move BP+ folder

* Correct no-std support

* Rename "long_n" to eta

* Add note on non-prime order dfg points

coins/monero/src/tests/bulletproofs/plus/aggregate_range_proof.rs

@@ -0,0 +1,30 @@
+use rand_core::{RngCore, OsRng};
+
+use multiexp::BatchVerifier;
+use group::ff::Field;
+use dalek_ff_group::{Scalar, EdwardsPoint};
+
+use crate::{
+  Commitment,
+  ringct::bulletproofs::plus::aggregate_range_proof::{
+    AggregateRangeStatement, AggregateRangeWitness,
+  },
+};
+
+#[test]
+fn test_aggregate_range_proof() {
+  let mut verifier = BatchVerifier::new(16);
+  for m in 1 ..= 16 {
+    let mut commitments = vec![];
+    for _ in 0 .. m {
+      commitments.push(Commitment::new(*Scalar::random(&mut OsRng), OsRng.next_u64()));
+    }
+    let commitment_points = commitments.iter().map(|com| EdwardsPoint(com.calculate())).collect();
+    let statement = AggregateRangeStatement::new(commitment_points).unwrap();
+    let witness = AggregateRangeWitness::new(&commitments).unwrap();
+
+    let proof = statement.clone().prove(&mut OsRng, witness).unwrap();
+    statement.verify(&mut OsRng, &mut verifier, (), proof);
+  }
+  assert!(verifier.verify_vartime());
+}