OpenAPI v3 "links components" seem broken

[dunglas]

#2414 seems to be broken, as least with version 2.4.

[bpolaszek]

Checked with @dunglas, link components are actually supported on POST operations only (resource creation).

Todo:

• Add support everywhere it could be needed
• Return Iri reference (@id) when possible.

[teohhanhui]

The implementation of #2419 was problematic as it made too many assumptions.

I'm trying to make getLinkObject pass the correct $options to the metadata factories, as part of #3425, but this is not possible because of the architecture (getLinkObject is only called in the context of the GET item operation, whereas we actually need the context of the operation for which the response is being computed).