Issue #2196907 by divesh.kumar: Convert all calls & docs references to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in link module.

Issue #2196901 by divesh.kumar, longwave: Convert all calls & docs references to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in language module.

Issue #2196897 by divesh.kumar: Convert all calls & docs references to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in image module.

Issue #2196895 by divesh.kumar: Convert all calls & docs references to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in forum module.

Issue #2196805 by divesh.kumar: Convert all calls to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in ban module.

Issue #2196801 by divesh.kumar: Convert all calls to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in aggregator module.

Issue #2196797 by divesh.kumar: Convert all calls to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in action module.

Issue #2196807 by longwave, divesh.kumar: Convert all calls to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in block module.