ParquetAvroFileOperations does not set dataSupplier

[clairemcginty]

Parquet-Avro will default to using a SpecificData model, which breaks GenericRecord reads if there's an available class on the classpath with the same name as the Avro schema due to SpecificData's class lookup implementation. In contrast, ParquetAvroIO in scio-parquet always sets dataSupplier for generic reads.

I put up a branch with a sample repro