Issue #1802278 by KarenS, andypost: Added a Date component to core.

core/includes/common.inc

core/lib/Drupal/Component/Datetime/DateTimePlus.php

core/lib/Drupal/Core/Datetime/DrupalDateTime.php

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

...ules/comment/lib/Drupal/comment/CommentFormController.php

core/modules/node/lib/Drupal/node/NodeFormController.php

core/modules/node/node.module

...tem/lib/Drupal/system/Tests/Datetime/DateTimePlusTest.php

...m/lib/Drupal/system/Tests/Datetime/DrupalDateTimeTest.php

...ystem/lib/Drupal/system/Tests/TypedData/TypedDataTest.php