bug(syntax): Ord on ast::Position is inconsistent with Eq #1393

What version of regex are you using?

0.8.11

Describe the bug at a high level.

Ord for Position is keyed off of offset only, but its Eq and PartialEq are derived, so they can disagree.

This affects Span as well, since it stores Positions.

The methods of this trait must be consistent with each other and with those of PartialEq.

https://doc.rust-lang.org/std/cmp/trait.PartialOrd.html

What are the steps to reproduce the behavior?

use std::collections::BTreeSet;
use regex_syntax::ast::{Position, Span};

fn main() {
    let a = Position { offset: 0, line: 1, column: 1 };
    let b = Position { offset: 0, line: 9, column: 9 };

    assert_ne!(a, b);
    assert_eq!(a.cmp(&b), std::cmp::Ordering::Equal);

    let mut set = BTreeSet::new();
    set.insert(a);
    set.insert(b);
    assert_eq!(set.len(), 1);
}

What is the actual behavior?

BTreeSet is confused, all assertions pass.

What is the expected behavior?

Both a and b are inserted.

Found with a fuzzer I'm developing.