[SPARK-54999] Re-enable ConstraintTests by moving into IcebergTests

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR re-enables the constraint test coverage (SPARK-51207, SPIP: Constraints in DSv2) that was disabled in SPARK-54998, by moving the four tests out of the disabled ConstraintTests suite into IcebergTests and switching them from USING ORC (DSv1) to USING ICEBERG (DSv2):

• primary_key, foreign_key, unique, and check now create local.db.* Iceberg tables and run under the existing SPARK_ICEBERG_TEST_ENABLED guard, like the other IcebergTests.
• The spark.version.starts(with: "4.1") guard is kept so the constraint syntax (a Spark 4.1+ feature) runs only on the Spark 4.1.2 Iceberg CI job and is skipped on the Spark 4.0.2 one.
• Tests/SparkConnectTests/ConstraintTests.swift is removed.
• Fix the foreign_key test to reference the parent table (tableName1, which has id) instead of the table being created.

Note that this is possible because we moved to Apache Iceberg 1.11.0.

• [SPARK-57010] Upgrade Iceberg to 1.11.0 in integration tests #376

Why are the changes needed?

ConstraintTests was disabled in SPARK-54998 because Spark 4.1.1+ started throwing on constraint syntax for DSv1 (ORC) tables after SPARK-54761, and the original plan was to revisit this with DSv2 tables once Apache Iceberg supported Spark 4.1. Iceberg now ships a Spark 4.1 runtime (iceberg-spark-runtime-4.1_2.13:1.11.0, already used by CI), so the constraint syntax can be validated against DSv2/Iceberg tables as originally intended.

Does this PR introduce any user-facing change?

No. This is a test-only change.

How was this patch tested?

Pass the CIs.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Claude Opus 4.8)

[dongjoon-hyun]

This is still a Draft.