Support Ruby 3.1 shorthand hash syntax

I'm primarily excited to be able to do this:

```ruby
a = "abc"
b = 123

hsh = {a:, b:}
```

as it's virtually identical to JS's `{a, b}` syntax. I also realized we don't yet support the other direction which I would like to tackle as well.

```ruby
hsh => {a:, b:}
```

should become

```js
let {a, b} = hsh
```