Add fullstack tests for BIT_OR.

Signed-off-by: RinChanNOWWW <rinchannow@bupt.edu.cn>

tests/fullstack-test/expr/agg_bit_or_pushdown.test

@@ -0,0 +1,76 @@
+# Copyright 2022 PingCAP, Ltd.
+#
+# Licensed 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.
+
+mysql> drop table if exists test.all_null
+mysql> create table test.all_null (a int, b int)
+mysql> alter table test.all_null set tiflash replica 1
+mysql> insert into test.all_null values(1, NULL), (1, NULL), (2, NULL), (2, NULL), (3, NULL);
+
+mysql> drop table if exists test.not_all_null
+mysql> create table test.not_all_null (a int, b int)
+mysql> alter table test.not_all_null set tiflash replica 1
+mysql> insert into test.not_all_null values(1, 1), (1, 2), (2, 2), (2, 4), (3, NULL), (3, 4);
+
+mysql> drop table if exists test.char
+mysql> create table test.char (a int, b char(10))
+mysql> alter table test.char set tiflash replica 1
+mysql> insert into test.char values(1, '1a'), (1, '2a2'), (2, '2bbb'), (2, '4ccc11'), (3, 'adasda'), (3, 'ASD');
+
+mysql> set @@tidb_isolation_read_engines='tiflash'
+
+mysql> select bit_or(b) from test.all_null;
++-----------+
+| bit_or(b) |
++-----------+
+|         0 |
++-----------+
+mysql> select a, bit_or(b) from test.all_null group by a;
++------+-----------+
+| a    | bit_or(b) |
++------+-----------+
+|    1 |         0 |
+|    2 |         0 |
+|    3 |         0 |
++------+-----------+
+
+
+mysql> select bit_or(b) from test.not_all_null;
++-----------+
+| bit_or(b) |
++-----------+
+|         7 |
++-----------+
+mysql> select a, bit_or(b) from test.not_all_null group by a;
++------+-----------+
+| a    | bit_or(b) |
++------+-----------+
+|    1 |         3 |
+|    2 |         6 |
+|    3 |         4 |
++------+-----------+
+
+mysql> select bit_or(b) from test.char;
++-----------+
+| bit_or(b) |
++-----------+
+|         7 |
++-----------+
+mysql> select a, bit_or(b) from test.char group by a;
++------+-----------+
+| a    | bit_or(b) |
++------+-----------+
+|    1 |         3 |
+|    2 |         6 |
+|    3 |         0 |
++------+-----------+