HV-900 Documenting Java 8 support

> I don't think @Valid is right here.

I think there is a miscommunication here. The type use validation is designed as part of the cascade routine. So `@Valid` must always be present to qualify the element as `Cascadable`. This is to satisfy the requirement of only iterating once.

To accomplish this, type use validation is performed in `ValidatorImpl#validateCascadedConstraints`.

Please see `Cascadable#getTypeArgumentsConstraints` and the tests in `TypeUseValidationTest`.