Entity manager deprecation fixes

1. +++ b/src/Plugin/migrate/process/EntityGenerate.php
   @@ -67,42 +71,14 @@ class EntityGenerate extends EntityLookup {
   -  public function __construct(array $configuration, $pluginId, $pluginDefinition, MigrationInterface $migration, EntityManagerInterface $entityManager, SelectionPluginManagerInterface $selectionPluginManager, MigratePluginManager $processPluginManager) {
   -    parent::__construct($configuration, $pluginId, $pluginDefinition, $migration, $entityManager, $selectionPluginManager);
   -    $this->processPluginManager = $processPluginManager;
   -  }
   

   While I very much support this constructor change, It may be disruptive, as EntityGenerate is very often extended in custom code. It might be better to leave BC shim in for now and make this change in a 8.x-5.x branch

2. +++ b/src/Plugin/migrate/process/EntityLookup.php
   @@ -142,14 +150,15 @@ class EntityLookup extends ProcessPluginBase implements ContainerFactoryPluginIn
   -  public function __construct(array $configuration, $pluginId, $pluginDefinition, MigrationInterface $migration, EntityManagerInterface $entityManager, SelectionPluginManagerInterface $selectionPluginManager) {
   +  public function __construct(array $configuration, $pluginId, $pluginDefinition, MigrationInterface $migration, EntityTypeManagerInterface $entityTypeManager, EntityFieldManagerInterface $entityFieldManager, SelectionPluginManagerInterface $selectionPluginManager) {
   

   switching to EntityTypeManagerInterface is okay, because EntityManagerInterface extends EntityTypeManagerInterface so this is a widening of acceptable parameters and not a BC break, but EntityFieldManagerInterface should be at the end and be nullable to prevent a BC break

I'd +1 on that being in a new 5.x branch; I do have around 8 plugins extending either EntityGenerate or EntityLookup in various migrations - some of which are regularly (cron) repeated.