Issue #3501186 by znerol, smustgrave: Change $previous argument for any Exception to \Throwable

...ent/Plugin/Exception/InvalidPluginDefinitionException.php

...al/Component/Plugin/Exception/PluginNotFoundException.php

core/lib/Drupal/Core/Database/RowCountException.php

core/lib/Drupal/Core/Form/EnforcedResponseException.php

...Drupal/Core/Form/Exception/BrokenPostRequestException.php

core/lib/Drupal/Core/Form/FormAjaxException.php

...ore/Http/Exception/CacheableAccessDeniedHttpException.php

.../Core/Http/Exception/CacheableBadRequestHttpException.php

...al/Core/Http/Exception/CacheableConflictHttpException.php

...Drupal/Core/Http/Exception/CacheableGoneHttpException.php

...lib/Drupal/Core/Http/Exception/CacheableHttpException.php

...e/Http/Exception/CacheableLengthRequiredHttpException.php

...Http/Exception/CacheableMethodNotAllowedHttpException.php

...re/Http/Exception/CacheableNotAcceptableHttpException.php

...al/Core/Http/Exception/CacheableNotFoundHttpException.php

...tp/Exception/CacheablePreconditionFailedHttpException.php

.../Exception/CacheablePreconditionRequiredHttpException.php

...tp/Exception/CacheableServiceUnavailableHttpException.php

.../Http/Exception/CacheableTooManyRequestsHttpException.php

...ore/Http/Exception/CacheableUnauthorizedHttpException.php