"Links" field not displaying on custom view modes

Problem/Motivation

When using a custom view mode, the "Links" field is not displayed.

Steps to reproduce:

1. Starting with a fresh D8 site.
2. Add a dummy node of type "Article".
3. Create a custom view mode for the "Article" content type.
4. Configure the new custom view mode to display the "Links" field.
5. Create a new view to show all nodes of type "Article", displaying "Content" with the new view mode.
6. See in the Views preview that no "Links" are displayed.

As additional confirmation, confirm that the "Links" field is visible in the "Teaser" display, then change the View to display the "Teaser" and note that the "Links" are displayed.

Proposed resolution

Properly display the Links field on custom view modes.

Remaining tasks

User interface changes

API changes

Data model changes