Postfix completion is broken in some cases

Previously reported in https://github.com/redhat-developer/vscode-java/issues/3088, but reproduced in Eclipse 2023-03 and latest 2023-06 milestone:

After enabling postfix completion, try completing on .var:

```java
public static void main(String[] args) {
Stream.iterate(0,i -> ++i).limit(10).var|
}
```
This results in:

```java
public static void main(String[] String[] args = args) {
Stream.iterate(0,i -> ++i).limit(10);
}
```

or
```java
public static void main(String[] args) {

Stream v = Stream.iterate(0,i -> ++i).limit(10);

v.collect(Collectors.toList()).var|
}
```

yields:

```java
public static void main(String[] args) {

Stream Stream v = v = Stream.iterate(0, i -> ++i).limit(10);

v.collect(Collectors.toList());
}
```

Other postfix completions generate equally broken code.