CriteriaBuilder doesn't work with ELEMENT_COLLECTION

I have a domain object with a collection of non-domain objects.
```
class Person{
static hasMany = [knownContacts: KnownContacts]
}

enum KnownContacts{
None,
Email,
Phone
}
```
I want to use this "association" in a criteria, but that throws a `groovy.lang.MissingMethodException: No signature of method` error at `knownContacts { ... }`.

```
{
projections {
knownContacts {
id()
}
}
}
```

This is because gorm treats the "knownContacts" not as an association, but as an ELEMENT_COLLECTION.
Which means the isAssociation check fails on it, as its PersistentAttributeType is ELEMENT_COLLECTION.
```
public boolean isAssociation() {
return getPersistentAttributeType() == PersistentAttributeType.ONE_TO_MANY
|| getPersistentAttributeType() == PersistentAttributeType.MANY_TO_MANY;
}
```
There doesn't seem to be any code in AbstractHibernateCriteriaBuilder.invokeMethod that deals with ELEMENT_COLLECTIONs.

```
if (pd != null && pd.getReadMethod() != null) {
final Metamodel metamodel = sessionFactory.getMetamodel();
final EntityType entityType = metamodel.entity(targetClass);
final Attribute attribute = entityType.getAttribute(name);

if (attribute.isAssociation())
[...]
```
The `attribute.isAssociation` check fails and the `throw new MissingMethodException(name, getClass(), args);` at the end of the method is reached.

I'm not sure if this is intentional or an oversight. Is there a different way we are supposed to query non domain to domain associations?

The generated database schema creates an extra table for ELEMENT_COLLECTION (at least in this case) so I'm not sure why they can't be used like regular associations between domain objects.

Reproduce the Person/knownContacts criteria projection with the enum-backed ELEMENT_COLLECTION example. Start in AbstractHibernateCriteriaBuilder.invokeMethod and inspect how the metamodel attribute and isAssociation check handle ELEMENT_COLLECTION. Done means establishing the intended query behavior and adding coverage for the knownContacts projection or documenting the supported alternative.

Written by the indexing model from the issue text.