This method is called by the REST input parsers to allow a field type to pre
process the given $incomingValidatorConfigurationHash before it is handled
by {@link eZ\Publish\SPI\FieldType\FieldType::validatorConfigurationFromHash()}.
The $incomingValidatorConfigurationHash can be expected to conform to the
rules that need to apply to hashes accepted by validatorConfigurationFromHash().
The return value of this method replaces the $incomingValidatorConfigurationHash.