Normalizers should not throw an errors

Normalizers should not throw an errors - we already have Validators for this purpose. Better return value as is in that case when normalizer can't perform normalization.
Also we should not analyse is this property required or not.
According to this information contract will be pretty simple
```
public function supports(Schema $propertySchema, string $propertyName): bool;
public function getNormalizer(): Closure;
```