Issue #1792800 by tim.plunkett: Move code out of handlers.inc.

includes/handlers.inc

lib/Drupal/views/ManyToOneHelper.php

lib/Drupal/views/Plugin/views/HandlerBase.php

...Drupal/views/Plugin/views/argument/ArgumentPluginBase.php

lib/Drupal/views/Plugin/views/argument/Date.php

lib/Drupal/views/Plugin/views/argument/ManyToOne.php

lib/Drupal/views/Plugin/views/argument/Numeric.php

lib/Drupal/views/Plugin/views/argument/String.php

lib/Drupal/views/Plugin/views/query/Sql.php

lib/Drupal/views/Plugin/views/sort/Date.php

lib/Drupal/views/Tests/Handler/HandlerTest.php

lib/Drupal/views/Tests/PluginInstanceTest.php

lib/Views/node/Plugin/views/argument/CreatedDay.php

lib/Views/node/Plugin/views/argument/CreatedFullDate.php

lib/Views/node/Plugin/views/argument/CreatedMonth.php

lib/Views/node/Plugin/views/argument/CreatedWeek.php

lib/Views/node/Plugin/views/argument/CreatedYear.php

lib/Views/node/Plugin/views/argument/CreatedYearMonth.php

lib/Views/node/Plugin/views/argument_validator/Node.php

lib/Views/taxonomy/Plugin/views/argument/IndexTidDepth.php