Add workaround support for dynamic_entity_reference fields

Closes #3441330

src/EntitySchemaBuilder.php

@@ -277,6 +277,9 @@ class EntitySchemaBuilder {
       // this field at all.
       return NULL;
     }
+    elseif ($fieldType === 'dynamic_entity_reference') {
+      return $field->type('Entity');
+    }
     elseif ($typedData instanceof TextWithSummaryItem) {
       $summary = $this->createField('summary')->type('Boolean');
       return $field->type('String')->argument($summary);
@@ -312,6 +315,15 @@ class EntitySchemaBuilder {
    */
   private function getTypeForEntityReferenceFieldItem(FieldItemDataDefinitionInterface $itemDefinition): ?string {
     $targetType = $itemDefinition->getSetting('target_type');
+    $dataType = $itemDefinition->getDataType();
+
+    // Special handling for the "dynamic_entity_reference" contrib module that
+    // allows referencing multiple different entity types in a field.
+    // Because we don't (yet) support union types, we just type these fields
+    // using the generic Entity interface.
+    if ($dataType === 'field_item:dynamic_entity_reference') {
+      return 'Entity';
+    }
 
     // Check if the target entity type is enabled.
     if (!$targetType || !$this->config->isEntityTypeEnabled($targetType)) {
@@ -868,6 +880,9 @@ class EntitySchemaBuilder {
       case 'config_dependencies':
         return 'MapData';
 
+      case 'dynamic_entity_reference':
+        return 'Entity';
+
       case '_core_config_info':
         return NULL;