Provide more context to initial values event

Problem/Motivation

This is now the second time I hit against an issue where having more context passed to the initial values event would be helpful.

When we call:

  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $item = $items[$delta];
    $value = $item->getEntity()->isNew() ? $this->getInitialValues() : $item->toArray();

we don't pass the FieldItem along.

This is a problem, because I've called createDuplicate(), which nulls out the entity id and now my pre-seeded values get deleted. Either don't check isNew, or pass the item along so I can return to the defaults dynamically provided to the address widget.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes