Field punning for record creation

[LightAndLight]

Example:

let x = 1 in
let y = 2 in
let z = 3 in
{ x, y, z }

should desugar to:

let x = 1 in
let y = 2 in
let z = 3 in
{ x = x, y = y, z = z }

[LightAndLight]

Bump; I found myself expecting this today.