instanceof (and probably other) checks don't refine with direct boolean comparison

`instanceof` always returns a boolean, depending on whether it's something is an instance of something or not.

works:

```js
class A {cool: () => {}}
class B {}
const a = new A
const what: A | B = a;
if (what instanceof A) {
what.cool();
}
```

doesn't:

```js
class A {cool: () => {}}
class B {}
const a = new A
const what: A | B = a;
if ((what instanceof A) === true) {
what.cool();
}
```