Computed class property with decorator missing `key`

```js
  class A{
    @decorators
    [x] = 1
  }
```

It seems valid in TS, but I'm not sure, when playing with [this example](https://github.com/tc39/proposal-decorators/issues/556), I found meriyah emits a `PropertyDefinition` with `key: null`, it can't be right.