ComplexDataDefinitionBase improperly removes 'propertyDefinitions' when serialized

Problem/Motivation

When data of type Map is serialized and then unserialized, it loses its propertyDefinitions because ComplexDataDefinitionBase::__sleep() unconditionally unsets them during serialization.

The method treats propertyDefinitions as a disposable cache in all cases:

public function __sleep(): array {
  $vars = get_object_vars($this);
  unset($vars['propertyDefinitions'], $vars['typedDataManager']);
  return array_keys($vars);
}

However, this assumption is only valid for EntityDataDefinition, where propertyDefinitions is a lazily-derived state computed from entity_field.manager. For MapDataDefinition, propertyDefinitions is authored state — explicitly set via setPropertyDefinition() — and cannot be reconstructed after unserialization.

This surfaces in any scenario where a MapDataDefinition gets serialized and unserialized during a request. For example, a form using #ajax and #process callbacks that references a Map definition will lose its property definitions after form rebuild.

Additionally, ListDataDefinition does not unset its itemDefinition during serialization, creating an inconsistency in how child definitions are handled across complex and list data types.

Steps to reproduce

$map_definition = MapDataDefinition::create()
  ->setPropertyDefinition('status', DataDefinition::create('string'));
$typed_data = \Drupal::service('typed_data_manager')->create($map_definition);

// Before serialization: property definitions exist.
$before = $typed_data->getDataDefinition()->getPropertyDefinitions();
// ['status' => DataDefinition(string)]

$typed_data = unserialize(serialize($typed_data));

// After serialization: property definitions are gone.
$after = $typed_data->getDataDefinition()->getPropertyDefinitions();
// [] — empty!

Proposed resolution

1. Remove ComplexDataDefinitionBase::__sleep() entirely. This allows the parent DataDefinition::__sleep() to handle serialization, which already excludes typedDataManager but preserves all other properties including propertyDefinitions.
2. Move the propertyDefinitions exclusion into EntityDataDefinition::__sleep(), where it is appropriate. Entity data definitions lazily compute their property definitions from the entity field manager, so they should continue to exclude them during serialization (they will be re-derived on access after unserialization).

This is the minimal change: MapDataDefinition (and any other ComplexDataDefinitionBase subclass with authored property definitions) now correctly preserves its state across serialization, while EntityDataDefinition retains its existing lazy-load optimization.

Remaining tasks

Review and commit.

User interface changes

None.

Introduced terminology

None.

API changes

None. ComplexDataDefinitionBase::__sleep() was an internal implementation detail. Subclasses that relied on this behavior (only EntityDataDefinition in core) now have their own implementation.

Data model changes

None.

Release notes snippet

Fixed a bug where MapDataDefinition lost its propertyDefinitions when serialized. The ComplexDataDefinitionBase::__sleep() method incorrectly treated authored property definitions as a disposable cache. The exclusion logic was moved to EntityDataDefinition, where property definitions are genuinely lazily derived and should not be serialized.