Hive: Align VARIANT type mapping with Hive 4.2 support (HIVE-29184)

[Mukvin]

Apache Iceberg version

1.11.0 (latest release)

Query engine

Spark

Please describe the bug 🐞

Hive 4.2 introduced basic VARIANT support via HIVE-29184, but Iceberg's
HiveSchemaUtil still maps Iceberg VARIANT to "unknown".

Problem

• Current mapping in HiveSchemaUtil.convertToTypeString returns "unknown" for Iceberg VARIANT.
• This diverges from Hive 4.2 capability and from user expectation in Hive environments where VARIANT is supported.

Proposal

• Update Hive schema conversion for Iceberg VARIANT to return "variant".
• Update unit tests accordingly.

Scope

• hive-metastore schema conversion only.
• No change to non-VARIANT mappings.

References

• HIVE-29184: Iceberg: Basic Variant type support in Hive (Python: TableScan Plan files API implementation without residual evaluation #6069)
• Iceberg PR Hive: Convert VARIANT to binary placeholder #15228 / Spark, Hive: Fix snapshot procedure for tables with Variant columns #15964 historical discussion

Willingness to contribute

• I can contribute a fix for this bug independently
• I would be willing to contribute a fix for this bug with guidance from the Iceberg community
• I cannot contribute a fix for this bug at this time

[RussellSpitzer]

I wouldn't consider this a bug :) since we did design it to do this. But we should definitely do the fix

[Mukvin]

Ok, thx for your reply, I will close this issue.