Provide a split method which doesn't consume the element used to split

[johnfercher]

The split method consumes the element used to split, how you can see in the code below. But in some cases would be nice to move the element to the "first or second slice" like the split_at method does, but to n slices.

The numpy library has a method like that.

https://play.rust-lang.org/?gist=94dd413054604e4efffa96a5e8ed72b5&version=stable&mode=debug&edition=2015

Code

#[derive(Clone, Debug)]
struct Delta {
    pub val: i32
}

fn main() {
    let mut v = vec![Delta{ val: 1 }, Delta{ val: 5 }, Delta{ val: 1 }];
    
    let new_v : Vec<Vec<Delta>> = v.split(|x| x.val > 4)
                    .into_iter()
                    .map(|x| x.to_vec())
                    .collect();
                    
    println!("{:?}", new_v);
}

Output

[[Delta { val: 1 }], [Delta { val: 1 }]]

New Split Method1 Output

[[Delta { val: 1 }, Delta { val: 5 }], [Delta { val: 1 }]]

New Split Method2 Output

[[Delta { val: 1 }], [Delta { val: 5 }, Delta { val: 1 }]]

[oskgo]

#67330 added the first case as split_inclusive