Inaccurate estimated rows in mixed CNF and DNF conditions

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
create table t( id int, a int, b int, index idx(id, a));
insert into t values (1, 1, 1), (2, 2, 2), (3, 3, 3), (4, 4, 4), (5, 5, 5);
insert into t select * from t where id<>2;
insert into t select * from t where id<>2;
insert into t select * from t where id<>2;
insert into t select * from t where id<>2;
analyze table t;
explain select * from t where ( id > 1 or ( a>0 and id=0 )) and ( id < 3 or ( a>0 and id=6 ));
```

### 2. What did you expect to see? (Required)

```
mysql> explain analyze select * from t use index(idx) where ( id > 1 or ( a>0 and id=0 )) and ( id < 3 or ( a>0 and id=6 ));
+-------------------------------+---------+---------+-----------+---------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------+---------+------+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
+-------------------------------+---------+---------+-----------+---------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------+---------+------+
| IndexLookUp_8 | 12.82 | 1 | root | | time:2.07ms, loops:2, index_task: {total_time: 1.26ms, fetch_handle: 1.25ms, build: 931ns, wait: 1.52µs}, table_task: {total_time: 647.6µs, num: 1, concurrency: 5}, next: {wait_index: 1.43ms, wait_table_lookup_build: 30.6µs, wait_table_lookup_resp: 583.9µs} | | 9.13 KB | N/A |
| ├─Selection_7(Build) | 12.82 | 1 | cop[tikv] | | time:1.25ms, loops:3, cop_task: {num: 1, max: 1.16ms, proc_keys: 1, rpc_num: 1, rpc_time: 1.14ms, copr_cache_hit_ratio: 0.00, distsql_concurrency: 15}, tikv_task:{time:0s, loops:1}, scan_detail: {total_process_keys: 1, total_process_keys_size: 55, total_keys: 4, get_snapshot_time: 34.4µs, rocksdb: {key_skipped_count: 1, block: {}}} | or(gt(test.t.id, 1), and(gt(test.t.a, 0), eq(test.t.id, 0))), or(lt(test.t.id, 3), and(gt(test.t.a, 0), eq(test.t.id, 6))) | N/A | N/A |
| │ └─IndexRangeScan_5 | 16.02 | 1 | cop[tikv] | table:t, index:idx(id, a) | tikv_task:{time:0s, loops:1} | range:[0,0], (1,3), [6,6], keep order:false | N/A | N/A |
| └─TableRowIDScan_6(Probe) | 12.82 | 1 | cop[tikv] | table:t | time:553.1µs, loops:2, cop_task: {num: 1, max: 456.2µs, proc_keys: 1, rpc_num: 1, rpc_time: 427.3µs, copr_cache_hit_ratio: 0.00, distsql_concurrency: 15}, tikv_task:{time:0s, loops:1}, scan_detail: {total_process_keys: 1, total_process_keys_size: 45, total_keys: 1, get_snapshot_time: 21.3µs, rocksdb: {block: {}}} | keep order:false | N/A | N/A |
+-------------------------------+---------+---------+-----------+---------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------+---------+------+
```

### 3. What did you see instead (Required)

```
explain select * from t where ( id > 1 or ( a>0 and id=0 )) and ( id < 3 or ( a>0 and id=6 ));
+-------------------------+---------+-----------+---------------+----------------------------------------------------------------------------------------------------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------+---------+-----------+---------------+----------------------------------------------------------------------------------------------------------------------------+
| TableReader_7 | 12.82 | root | | data:Selection_6 |
| └─Selection_6 | 12.82 | cop[tikv] | | or(gt(test.t.id, 1), and(gt(test.t.a, 0), eq(test.t.id, 0))), or(lt(test.t.id, 3), and(gt(test.t.a, 0), eq(test.t.id, 6))) |
| └─TableFullScan_5 | 65.00 | cop[tikv] | table:t | keep order:false |
+-------------------------+---------+-----------+---------------+----------------------------------------------------------------------------------------------------------------------------+
```

The total selectivity is the product of the selectivities of the two CNF items, then the estRows equals `65 * (49/65) * (17/65) = 12.82`, but the ranges `id > 1, id < 3` for the column id can probably be merged.
```
mysql> explain select * from t where ( id > 1 or ( a>0 and id=0 ));
+-------------------------+---------+-----------+---------------+--------------------------------------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------+---------+-----------+---------------+--------------------------------------------------------------+
| TableReader_7 | 49.00 | root | | data:Selection_6 |
| └─Selection_6 | 49.00 | cop[tikv] | | or(gt(test.t.id, 1), and(gt(test.t.a, 0), eq(test.t.id, 0))) |
| └─TableFullScan_5 | 65.00 | cop[tikv] | table:t | keep order:false |
+-------------------------+---------+-----------+---------------+--------------------------------------------------------------+
3 rows in set (0.00 sec)

mysql> explain select * from t where ( id < 3 or ( a>0 and id=6 ));
+-------------------------+---------+-----------+---------------+--------------------------------------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------+---------+-----------+---------------+--------------------------------------------------------------+
| TableReader_7 | 17.00 | root | | data:Selection_6 |
| └─Selection_6 | 17.00 | cop[tikv] | | or(lt(test.t.id, 3), and(gt(test.t.a, 0), eq(test.t.id, 6))) |
| └─TableFullScan_5 | 65.00 | cop[tikv] | table:t | keep order:false |
+-------------------------+---------+-----------+---------------+--------------------------------------------------------------+
3 rows in set (0.00 sec)
```

### 4. What is your TiDB version? (Required)

v6.5.11