Parquet: add variant type support

[aihuaxu]

This is to enable writing Variant data to Parquet file and read from Parquet file in the format of struct of metadata and data.

This PR adds:

• A Parquet Variant implementation which currently uses Spark-Variant library as the dependency. We can reimplement inside the Iceberg-Core library to remove such dependency for now before that is moved to Parquet project.
• Add necessary Variant support in Parquet reader/writer.

TODO:

1. Add more test coverage.
2. Implement Variant encoding/decoding to remove Spark-Variant library dependency.
3. Add Parquet logical type Variant so ParquetTypeVisitor can understand Variant type from Parquet annotation.

Part of: #11178.

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[github-actions]

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