EntityReferenceRevisionsItem prematurely loads referenced entities

Problem/Motivation

I first reported in #3558370: Expand preloading in formatter

We prematurely load all ERR referenced entities when ::load() or ::loadeMultiple is called. In our case, we're loading several hundreds of entities with base fields in a JSON::API feed. What we'd rather have happen is delay loading all the ERR entities until later, at which point we'll load them all in a ::loadMultiple(). We've got things tuned so we have one ::loadMultiple() that loads up 500 entities at a time in (1) query. Because of this erring code, that results in 1+500 additional queries for each of the ERR fields. Whereas if this delayed the loading until later, we'd only have (2) queries.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes