Keep annotations on generated declarations

Would be great if

```kotlin
@MutableImpl(annotationPackages = [foo.Bar::class])
interface Sample {
   @foo.Bar
    val sample: String
   @get:foo.Baz
    val number: Int
}
```

generated

```kotlin
class MutableSample(
   @foo.Bar
   public override var sample: String,
   @get:foo.Baz
   public override var number: Int
) : Sample
```

Happy to add a PR!