Poly-commitment: rename elems into chunks [develop] - DON'T MERGE

[dannywillems]

Backporting from master
See #2658

[volhovm]

Looks good. There are just a few other lines that could be /also/ renamed:

ї> git grep elems
poly-commitment/src/commitment.rs:        let elems_size = Iterator::max(com.iter().map(|c| c.chunks.len())).unwrap();
poly-commitment/src/commitment.rs:        let mut chunks = Vec::with_capacity(elems_size);
poly-commitment/src/commitment.rs:        for chunk in 0..elems_size {
poly-commitment/src/srs.rs:    let t = G::BaseField::from_base_prime_field_elems(&base_fields).unwrap();
poly-commitment/src/srs.rs:        let num_elems = (n + srs_size - 1) / srs_size;
poly-commitment/src/srs.rs:        let mut chunks = Vec::with_capacity(num_elems);
poly-commitment/src/srs.rs:        for i in 0..num_elems {
poly-commitment/src/srs.rs:            // Append the 'partial Langrange polynomials' to the vector of elems chunks

[dannywillems]

Closing as it is done in upstream PR #2868