MapContextDefinition not properly setting property definitions for validation

Problem/Motivation

The \Drupal\tool\TypedData\MapContextDefinition::getDataDefinition() method isn't properly taking advance of the map data types property definitions.

Steps to reproduce

 $test = new MapContextDefinition(
      data_type: 'map',
      required: TRUE,
      multiple: TRUE,
      value_definitions: [
        'value1' => new ContextDefinition(
          data_type: 'string',
          label: $this->t('Value 1'),
          required: TRUE
        ),
        'value2' => new ContextDefinition(
          data_type: 'integer',
          label: $this->t('Value 2'),
          required: TRUE
        ),
      ]
    );
    $context = new Context($test, [['value1' => null, 'value2' => 3]]);
    $violations = $context->validate();

Proposed resolution

Fix.