feat: support current timezone (apache#4348)

Author: YutaLin

docs/source/contributor-guide/spark_expressions_support.md

@@ -220,7 +220,7 @@
 - [ ] current_date
 - [ ] current_time
 - [ ] current_timestamp
-- [ ] current_timezone
+- [x] current_timezone
 - [x] date_add
 - [x] date_diff
 - [x] date_format

docs/source/user-guide/latest/expressions.md

@@ -101,6 +101,7 @@ of expressions that be disabled.
 
 | Expression       | SQL                          |
 | ---------------- | ---------------------------- |
+| CurrentTimeZone  | `current_timezone`           |
 | DateAdd          | `date_add`                   |
 | DateDiff         | `datediff`                   |
 | DateFormat       | `date_format`                |

spark/src/test/resources/sql-tests/expressions/datetime/current_timezone.sql

@@ -0,0 +1,40 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+statement
+CREATE TABLE test_current_timezone(id INT) USING parquet
+
+statement
+INSERT INTO test_current_timezone VALUES (1), (2), (3), (4), (NULL)
+
+query
+SELECT current_timezone()
+
+query
+SELECT current_timezone() IS NOT NULL
+
+query
+SELECT current_timezone() = current_timezone()
+
+query
+SELECT length(current_timezone()) > 0
+
+query
+SELECT id, current_timezone() IS NOT NULL FROM test_current_timezone
+
+query
+SELECT id FROM test_current_timezone WHERE current_timezone() = current_timezone()