isolatedDeclaration: dropping types used in declare module blocks

When using `isolatedDeclaration` transform:

In:

```ts
import { type X } from './x'

type Y = 1

declare module "foo" {
  interface Foo {
    x: X
    y: Y
  }
}
```

Out (see that import of `X` and declaration of `Y` are both incorrectly removed):

```ts
declare module "foo" {
	interface Foo {
		x: X;
		y: Y;
	}
}
export {};
```