Cacheability metadata can't be set from within argument default handlers.

Problem/Motivation

For this particular site we have a feature called "featured content" which is a node reference for each term. These then appear at the top of the term page.
Sadly cacheability metadata wasn't picked up, when set to $this->view->element

Proposed resolution

Ensure that we carry over the cacheability metadata.

Remaining tasks

User interface changes

API changes

Data model changes