Replace Title::isWatchable() with WatchlistManager::isWatchable()

[cicalese]

Title::isWatchable is deprecated in MediaWiki 1.37.

Replace it in ReviewHandler.php and SpecialPageStatistics.php.

Replace:

$title->isWatchable()

with:

MediaWikiServices::getInstance()->getWatchlistManager()->isWatchable( $title ) )