ParentValueContainer.getConversionContainer does not handle FIXED schema types properly

ParentValueContainer.getConversionContainer attempts to convert the value to (GenericData.Fixed) instead of the more broad (GenericFixed) class. GenericData.Fixed implements GenericFixed, and GenericFixed is the avro class that should be used instead of the more specific parquet-avro GenericData.Fixed.

**Environment**: Windows 10, Flink, IntelliJ IDE
**Reporter**: [Daniel Steffy](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=steffyd)

_{**Note**: *This issue was originally created as [PARQUET-1486](https://issues.apache.org/jira/browse/PARQUET-1486). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}