Optimize DatataObject.hashCode()

We currently generate the following code for single-entry classes:

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + Objects.hashCode(_lockName);
        return result;
    }

This is wasteful, as we could simply delegate to _lockName(), which could be caching hashCode (as String does), thus arithmetics from hashCode().

We should end up with:

    @Override
    public int hashCode() {
        return Objects.hashCode(_lockName);
    }

which is a change in hashCode() specification, hence runtime needs to be updated accordingly.