Array spreading still uses Belt

[nojaf]

See playground

let x = [ "a" ]
let y = [ ...x]

generates

// Generated by ReScript, PLEASE EDIT WITH CARE
'use strict';

let Belt_Array = require("./stdlib/belt_Array.js");

let x = ["a"];

let y = Belt_Array.concatMany([x]);

exports.x = x;
exports.y = y;
/* y Not a pure module */

I would expect Belt no longer be used for this. Given concatMany exists in Core.

With some pointers, I would be interested in taking a stab at this myself.

[zth]

This will be fixed as Core moves into the compiler in v12.

[nojaf]

Oh, I see, thanks for pointing that out!

[cknitt]

This is already tracked in #6836.