Silently ignore missing entity references instead of triggering an exception

Problem/Motivation

When entity references break because of deleted referenced entities, it could be better to not trigger an exception and silently ignore the entity in the decoupled output.

Proposed resolution

Add a configuration checkbox in the module settings to choose whether the formatters break or ignore the entity in the output.

Edit EntityReferenceDecoupledFormatterBase::viewMultivaluedFieldItemList() to ignore InvalidContentException.