Add (immutable) sort to Array

[cknitt]

• sort is the immutable version of the JS Array.sort function
• stableSort, stableSortInPlace are the implementation from Belt
• Use Array.sortInPlace for List.sort

[cknitt]

It seems we do not need our own stable sort implementation.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#sort_stability

Since version 10 (or ECMAScript 2019), the specification dictates that Array.prototype.sort is stable.

[zth]

We'll do docstrings when doing the rest of the module.