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

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)