Deep references lose langcode during formatting

Problem/Motivation

1. Entity A has a translation in language L. It refers entity B and the reference field is formatted using entity_reference_entity_view
2. Entity B does not have a translation in language L. It refers entity C and the reference field is formatted using entity_reference_entity_view
3. Entity C has a translation in language L.

In this case, when viewing Entity A in language L, Entity C will not be in the correct language.

The root cause is EntityReferenceEntityFormatter::viewElements() rendering the referred entity in the parent entity langcode. But the parent entity might be in a fallback langcode.

Steps to reproduce

1. Have German set up besides and English.
2. Add a node reference field to a node type,
3. Set the formatter to "Rendered entity"
4. Create a node with German and English translations.
5. Create another English node, set the reference field to point to the previous node. Do not translate this one.
6. Create another node, set the reference field to point to the previous node. Translate this one to German.

Viewing the last node in German will render the first node in English.

Proposed resolution

Pass the langcode down the chain. The patch is much smaller than this issue summary :) (The test isn't.)

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet