Add support for Primary Entity Reference fields (and others that extend Entity Reference?)

Problem/Motivation

Primary Entity Reference (like some other modules that extend core's Entity Reference) tracks some additional data (whether a given delta is the "primary" value), but is otherwise extremely similar to Entity Reference.

CorrespondingReferenceForm->getReferenceFieldMap contains:
$map = $this->fieldManager->getFieldMapByFieldType('entity_reference');

This returns only core Entity Reference fields (rather than fields of any field type that extends EntityReferenceItem) so CER doesn't support Primary Entity Reference (and its cousins).

Steps to reproduce

Proposed resolution

Either hardcode some additional field type IDs (including primary_entity_reference), or fetch the list of field types that extend EntityReferenceItem and use their field type IDs. If certain ones are known to not work this way (e.g. I suspect Dynamic Entity Reference might not), those could be excluded until explicitly supported.

Remaining tasks

User interface changes

API changes

Data model changes