JVMS changes for Records (Preview)

the current definition of the record attribute is:
```
Record_attribute {
    u2 attribute_name_index;
    u4 attribute_length;
    u2 components_count;
    record_component_info components[components_count];
}
```

where record_component_info is:
```
    record_component_info {
        u2 name_index;
        u2 descriptor_index;
        u2 attributes_count;
        attribute_info attributes[attributes_count];
    }
```

If the component has a generic signature that is different from the erased descriptor, it is placed in a Signature attribute on the component, similarly as we do for field_info at present.