Issue #2216553 by jhodgdon, fago: Fill in @defgroup/topic docs for Typed Data.

core/lib/Drupal/Core/TypedData/Annotation/DataType.php

.../Drupal/Core/TypedData/ComplexDataDefinitionInterface.php

core/lib/Drupal/Core/TypedData/ComplexDataInterface.php

core/lib/Drupal/Core/TypedData/DataDefinitionInterface.php

...rupal/Core/TypedData/DataReferenceDefinitionInterface.php

...lib/Drupal/Core/TypedData/ListDataDefinitionInterface.php

core/lib/Drupal/Core/TypedData/ListInterface.php

core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php

core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php

core/lib/Drupal/Core/TypedData/PrimitiveInterface.php

core/lib/Drupal/Core/TypedData/Type/BinaryInterface.php

core/lib/Drupal/Core/TypedData/Type/DateTimeInterface.php

core/lib/Drupal/Core/TypedData/Type/DurationInterface.php

core/lib/Drupal/Core/TypedData/Type/FloatInterface.php

core/lib/Drupal/Core/TypedData/Type/IntegerInterface.php

core/lib/Drupal/Core/TypedData/Type/StringInterface.php

core/lib/Drupal/Core/TypedData/Type/UriInterface.php

core/lib/Drupal/Core/TypedData/TypedData.php

core/lib/Drupal/Core/TypedData/TypedDataInterface.php

core/modules/system/core.api.php