Implement support for CompositeUserType and re-enable tests that make use of it

[beikov]

See #3960

Citing from the migration guide:

The CompositeUserType interface was re-implemented to be able to model user types as proper embeddable types.
A major difference to 5.x is the introduction of an "embeddable projection" that is used to determine the mapping structure.

Previously, a CompositeUserType had to provide property names and types through dedicated accessor methods,
but this was complicated for non-basic mappings and required quite some knowledge about Hibernate internals.
With 6.0 these methods are replaced with a method that returns an "embeddable projection" class.
The class is like a regular @Embeddable class and is used to determine the mapping structure for the CompositeUserType.

Component values of a user type object are accessed by property index. The property index is 0-based and can be determined
by sorting the persistent attribute names lexicographically ascending and using the 0-based position as property index.

For example, the following component:

public class MonetaryAmountEmbeddable {
	BigDecimal value;
	Currency currency;
}

will assign property index 0 to currency and index 1 to value.

Note that it is not possible anymore to use @Columns to specify the names of columns of a composite user type mapping.
Since a CompositeUserType now constructs a proper component, it is necessary to use the @AttributeOverride annotation.

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