Casted receiver completion doesn't work properly with array types

Consider completion after the `|` in the following class:

```java
public class DemoClass {
public void myMethod() {
Object obj = new Object();
if (obj instanceof DemoClass[]) {
obj.len|
}
}
}
```

the `length` completion item completes to:

```java
public class DemoClass {
public void myMethod() {
Object obj = new Object();
if (obj instanceof DemoClass[]) {
((DemoClass)obj).length
}
}
}
```

It's casted to `DemoClass` instead of `DemoClass[]`, which results in a compilation error.

There is at least two tests that assert that this behaviour is correct: `CompletionTests.testCompletionAfterInstanceof24_1` and `CompletionTests.testCompletionAfterInstanceof24_2`