Enhance public type system APIs to include missing parts

The already available public APIs for modification of type system like artifact types, attributes, data types, link types… are already allowing access to the main parts of type system.

Nevertheless, there are some parts missing:

• Link constraints: We also have the need for all CRUD operations for link constraints, like for all other type system resources to be able to read, create, change, and delete them. Please consider, that our link constraints are mainly defined cross-component, so there is a global context necessary or the option to set them with unresolved target.
• Link Validity: as we are usually enabling Link Validity together with the type system setup, we would like to also activate Link Validity through API. Please also consider idea ENGRMDN-I-831 with respect to Link Validity setting.
• Type system propagation: Overall bulk type system changes seem to be feasible for multiple streams. But we did not find the possibility to automate the “accept changes” or “deliver changes” mechanism from one variant stream to other variant streams. So that the same change set(s) containing the desired changes is/are propagated automatically to the desired variant streams. So individual bulk changes seem to be possible, but variant bulk changes (where you want to apply one or multiple identical change sets over variants) seems to fall short. We are following here IBM proposal with using a type system stream per component from which the type system changes shall be delivered to the real project / variant streams.