Issue #2216527 by sun: Inject a serialization format into database key/value storage.

core/core.services.yml

core/lib/Drupal/Component/Serialization/Json.php

core/lib/Drupal/Component/Serialization/PhpSerialize.php

core/lib/Drupal/Core/KeyValueStore/DatabaseStorage.php

...ib/Drupal/Core/KeyValueStore/DatabaseStorageExpirable.php

...l/Core/KeyValueStore/KeyValueDatabaseExpirableFactory.php

...lib/Drupal/Core/KeyValueStore/KeyValueDatabaseFactory.php

...stem/Tests/KeyValueStore/DatabaseStorageExpirableTest.php

...Drupal/system/Tests/KeyValueStore/DatabaseStorageTest.php

...upal/system/Tests/KeyValueStore/GarbageCollectionTest.php

core/modules/user/lib/Drupal/user/TempStoreFactory.php

...ules/user/lib/Drupal/user/Tests/TempStoreDatabaseTest.php