Monomorphize custom types

When the Gren compiler encounters a custom type like:

type Something
  = None
  | One Int
  | Two Int Int

It compiles it into (pseudo code)

var $namespace$None = { $: 'None' };

var $namespace$One = function(a) { return { $: 'One', a: a }; };

var $namespace$Two = function(a, b) { return { $: 'Two', a: a, b: b }; };

This means that the different constructors of Something return different types in the eyes of the JS JIT compiler. This again means that the performance of the code will be sub-optimal.

It would be better if the above Gren code produced something like:

var $namespace$Something = function(tag, a, b) {
  this.$ = tag;
  this.a = a;
  this.b = b;
};

var $namespace$None = new $namespace$Something('None', 0, 0);

var $namespace$One = function(a) { return new $namespace$Something('One', a, 0); };

var $namespace$Two = F2(function(a, b) { return new $namespace$Something('Two', a, b); });

The issue does not name specific files or tests. Start by locating the compiler entry point that generates JavaScript for custom types and inspect the constructor output for the shown Something example. Done means constructors share one representation while preserving the existing tags and fields, with relevant compiler tests passing.