Support query delegates on collection classes

[edudar]

Originally filed as querydsl/querydsl#3327

@QueryDelegate is a powerful feature that does not work properly with collections. QueryDSL creates Q-classes, but they extend BeanPath. As a result, one can't use expressions already available in these classes and can't pass appropriately typed Path parameters to custom extensions.

Actual:

public class QSet extends BeanPath<Set<?>> {
  ...
}

Expected:

public class QSet<V, E extends SimpleExpression<V>> extends SetPath<V, E> {
  ...
} 

public class QEntity extends BeanPath<Entity> {
  public final QSet<String, ext.java.lang.QString> s = 
    new QSet<String, ext.java.lang.QString>(forProperty("s"));
}

I tried to tinker around the annotation processor, but it does not look like it generally supports the generation of parameterized classes.