[SPARK-52268] Add variant SQL test and answer file

### What changes were proposed in this pull request?

This PR aims to add `variant` (SPARK-45891) SQL test and answer file with `parse_json` and `variant_get` methods.

### Why are the changes needed?

To add a test coverage for Spark 4 feature.

Note that this PR doesn't aim to cover `collect` with the serialization.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Pass the CIs.

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

No.

Closes #167 from dongjoon-hyun/SPARK-52268.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

Tests/SparkConnectTests/Resources/queries/variant.sql

@@ -0,0 +1,5 @@
+FROM VALUES parse_json('{"a": true, "b": 1, "c": "swift"}') T(v)
+|> SELECT v,
+          variant_get(v, '$.a', 'boolean') as a,
+          variant_get(v, '$.b', 'int') as b,
+          variant_get(v, '$.c', 'string') as c

Tests/SparkConnectTests/Resources/queries/variant.sql.answer

@@ -0,0 +1,5 @@
++----------------------------+----+---+-----+
+|                           v|   a|  b|    c|
++----------------------------+----+---+-----+
+|{"a":true,"b":1,"c":"swift"}|true|  1|swift|
++----------------------------+----+---+-----+

Tests/SparkConnectTests/SQLTests.swift

@@ -85,6 +85,7 @@ struct SQLTests {
     "create_table_function.sql",
     "pipesyntax.sql",
     "explain.sql",
+    "variant.sql",
   ]
 
 #if !os(Linux)