Map Field collection module's fieldformatters from D7 to Paragraphs in D8/D9.

This is okay!

Can confirm that this issue leads to an error during migration, after which the converted paragraph is not attached to the entity's view; to help out others looking for this, the error thrown during migration is:

[error] The "field_collection_fields" plugin does not exist. Valid plugin IDs for Drupal\Core\Field\FormatterPluginManager are:...

I can also confirm that the solution proposed above works. I should point out that there is a third formatter in D7 field_collection — "field_collection_list" — so a full solution should probably include this, e.g.:

  public function getFieldFormatterMap() {
    return [
      'field_collection_view' => 'entity_reference_revisions_entity_view',
      'field_collection_list' => 'entity_reference_revisions_entity_view',
      'field_collection_fields' => 'entity_reference_revisions_entity_view',
    ] + parent::getFieldFormatterMap();
  }

Let's update it then.

Re-rolled with suggested changes

I'm using this patch via paragraphs_migration -- I generated a set of migrations with migrate_plus, then customized upgrade_d7_field_formatter_settings.yml with the "field_collection_list" modification described in #4-- but upgrade_d7_field_formatter_settings is still failing. Every one of the view modes that include a field collection generates this type of message:

node 	event_program 	default 	field_added_item 	1 	Missing required properties for an EntityDisplay entity.
node 	event_program 	teaser 	field_added_item 	1 	Missing required properties for an EntityDisplay entity.

Is this an issue with the patch, or am I doing something wrong? (And if I am doing something wrong, please point me in the right direction to fix it, because that error message is a mystery -- if I try to just continue onwards without fixing it, I get similar errors on upgrade_d7_field_instance_widget_settings, and it is all downhill from there. Really stuck.)