Class statics doesn't get inherited in $ReadOnly

```js
class D {
static d: number = 0;
}
class M extends D {
static m: number = 1;
}

type S = $ReadOnly>;
type T = Class;

declare var t: T;

(t.m: number); // no error
(t.d: number); // no error

declare var s: S;

(s.m: number); // no error
(s.d: number); // error
```

Flow version: 0.95.1

## Expected behavior

No errors

## Actual behavior

* Link to Try-Flow or Github repo:
https://flow.org/try/#0MYGwhgzhAEAi0G8BQ1oQC5nQS2NAJgFzQB2ArgLYBGApgE7QC80ADANxIC+SokMAstBoAPdDRL4Y8ZKgxZc0CsXLV6TaAEYO3JEnQBPAA41oAZXUASAEo0w+APIkQ+gDwBhcFBf8AfD44GxtAAKuoefN7+uvg0vHQmAG5gDOjEwRxIABToAHRKpJS0dACUbNAA9OWkAPZCdHTVdFm5RAWqJWWVNXUNTUgxcYnJaMSmGZkQecqF9KUVVSS19L1Zk60qRXNdy41AA