Fix type inferencing and syntax highlighting for `@Category` method `this` and `super` within gstring

Consider the following:
```groovy
@Category(Type)
class C {
  def m() {
    "$this ${this.name} ${super.name}"
  }
}
```

![image](https://user-images.githubusercontent.com/18193802/149862333-bc82995f-5cd1-4020-aa21-0b7dfdeab061.png)