Fixed some PHPDoc issues
EZP-20848: SearchHandler throws InvalidArgumentException is Criterion/Query is not valid
EZP-20848: load only searchable fields and throw InvalidArgumentException when Field criterion target is not applicable
Removed deprecated TODO
EZP-20848: throw NotImplementedException when Legacy Storage does not implement search on a field
EZP-20848: check only searchable fields and throw InvalidArgumentException if Field criterion target is not applicable
EZP-20848: findSingle() and findContent() throw InvalidArgumentException if criterion/query is not valid