Computed property names in object destructuring

[bmeurer]

The current grammar doesn't support computed property names in object destructuring, for example

const {[Symbol.iterator]: iterator} = array;

is valid JavaScript (and TypeScript), but CodeMirror gets highly confused about what it's looking at.

cc @jaro-sevcik

[marijnh]

I didn't even know that was a thing! Attached patch adds support.

[bmeurer]

Wow, thanks!