Issue #1938380 by damiankloip, dawehner: Let ViewExecutable->preview() return a render array.

...y/lib/Drupal/history/Tests/Views/HistoryTimestampTest.php

.../rest/lib/Drupal/rest/Plugin/views/display/RestExport.php

.../rest/lib/Drupal/rest/Tests/Views/StyleSerializerTest.php

core/modules/views/includes/ajax.inc

...modules/views/lib/Drupal/views/Plugin/views/area/View.php

...b/Drupal/views/Plugin/views/display/DisplayPluginBase.php

...s/views/lib/Drupal/views/Tests/Handler/AreaEntityTest.php

...modules/views/lib/Drupal/views/Tests/Handler/AreaTest.php

...es/views/lib/Drupal/views/Tests/Handler/FieldUnitTest.php

...les/views/lib/Drupal/views/Tests/Handler/FieldWebTest.php

...modules/views/lib/Drupal/views/Tests/Plugin/CacheTest.php

...dules/views/lib/Drupal/views/Tests/Plugin/DisplayTest.php

.../views/lib/Drupal/views/Tests/Plugin/StyleMappingTest.php

...modules/views/lib/Drupal/views/Tests/Plugin/StyleTest.php

...ws/lib/Drupal/views/Tests/Plugin/StyleUnformattedTest.php

...les/views/lib/Drupal/views/Tests/UI/CustomBooleanTest.php

core/modules/views/lib/Drupal/views/Tests/ViewRenderTest.php

...upal/views_test_data/Plugin/views/display/DisplayTest.php

core/modules/views/views.module

core/modules/views/views_ui/lib/Drupal/views_ui/ViewUI.php