Spark, Hive: Fix snapshot procedure for tables with Variant columns

[nssalian]

Fixes: #14123 and #15220 too.

Summary

The snapshot procedure fails on Spark tables with Variant columns because the Hive catalog stores LazySimpleSerDe instead of ParquetHiveSerDe for these tables. The SerDe-based format detection doesn't recognize it and throws.
After fixing that, a second failure occurs when running the test provided in the issue, HiveSchemaUtil.convertToTypeString which has no case for VARIANT.

Changes

This adds a resolveFileFormat helper that falls back to table.provider() when the SerDe doesn't match a known format, and maps VARIANT to "unknown" in the Hive schema conversion, following the conversation here: #15228

Made changes in Spark v4.0 and v4.1

Test plan

• Expanded the test in the issue to include both partitioned and unpartitioned tables in both Spark 4.0 and 4.1 - skipped for hive and spark catalog until hive 4 lands
• Added a unit test for the HiveSchemaUtil conversion check

[nssalian]

@RussellSpitzer @pvary @aihuaxu @steveloughran @huaxingao PTAL

[steveloughran]

@nssalian will do