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.*}

从 ParentValueContainer.getConversionContainer 开始，检查 FIXED schema 值是如何转换的。确认转换接受更宽泛的 GenericFixed 类型，而不仅仅是 GenericData.Fixed，然后验证 FIXED 值在处理时不会出现报告的类型不匹配问题。

由索引模型根据 Issue 内容生成。