HIVE-29287: Iceberg: Variant Shredding support

[deniskuzZ]

What changes were proposed in this pull request?

Support for variant shredding, enabling Hive to write shredded variant data into Iceberg tables.

Ideally, this should follow the approach described in the reader/writer API proposal for Iceberg V4, where an execution engine provides the shredded writer schema.

As an interim solution, this PR introduces a writer that infers the shredded schema from the sample record captured before the Parquet writer is initialized.

Why are the changes needed?

Enables data skipping (predicate pushdown)

Does this PR introduce any user-facing change?

No

How was this patch tested?

variant_type_shredding.q

[deniskuzZ]

same thing as apache/iceberg#14297

[deniskuzZ]

PPD is not supported here, would be addressed in a separate JIRA

[sonarqubecloud]

Quality Gate passed

Issues
27 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[kokila-19]

I tested variant_type_shredding.q by removing 'variant.shredding.enabled'='true' from the table properties, and the qtest still passes without any failures.
This test verifies that basic INSERT/SELECT operations succeed with VARIANT columns but not actual shredding in the file.
This testing is not possible in qtest.

so maybe we can add a JUnit test (e.g., TestVariantShredding) that:
Writes VARIANT data with variant.shredding.enabled=true and false
Opens the resulting Parquet files via ParquetFileReader
Asserts that the typed_value field is present/absent accordingly