Unclear range scope in the execution plan

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
```sql
create table t1 (a varchar(20), b int, index (a)) collate utf8mb4_general_ci;
insert into t1 values ('南京', 1 ), ('南海', 2 );
explain select * from t1 use index (a) where a like '南%';
explain select * from t1 use index (a) where a = '南海';
```

### 2. What did you expect to see? (Required)
```sql
[16:13:38]TiDB root:test> explain select * from t1 use index (a) where a like '南%';
+---------------------------+---------+-----------+----------------------+----------------------------+
| id | estRows | task | access object | operator info |
+---------------------------+---------+-----------+----------------------+----------------------------+
| IndexLookUp_8 | 1.60 | root | | |
| ├─Selection_7(Build) | 1.60 | cop[tikv] | | like(test.t1.a, "南%", 92) |
| │ └─IndexFullScan_5 | 2.00 | cop[tikv] | table:t1, index:a(a) | keep order:false |
| └─TableRowIDScan_6(Probe) | 1.60 | cop[tikv] | table:t1 | keep order:false |
+---------------------------+---------+-----------+----------------------+----------------------------+
4 rows in set
Time: 0.007s
[16:13:45]TiDB root:test> explain select * from t1 use index (a) where a = '南海';
+---------------------------+---------+-----------+----------------------+-----------------------------------------+
| id | estRows | task | access object | operator info |
+---------------------------+---------+-----------+----------------------+-----------------------------------------+
| IndexLookUp_7 | 1.00 | root | | |
| ├─IndexRangeScan_5(Build) | 1.00 | cop[tikv] | table:t1, index:a(a) | range:["南海","南海"], keep order:false |
| └─TableRowIDScan_6(Probe) | 1.00 | cop[tikv] | table:t1 | keep order:false |
+---------------------------+---------+-----------+----------------------+-----------------------------------------+
3 rows in set
Time: 0.004s
```
### 3. What did you see instead (Required)
After support like range scan, the not correspond to legal characters sort keys will appear in the range.
you can see the `range:["SW","SW"]` is not easy to correlate with filter conditions
```sql
[15:48:41]TiDB root:test> explain select * from t1 use index (a) where a like '南';
+---------------------------+---------+-----------+----------------------+---------------------------------------------------+
| id | estRows | task | access object | operator info |
+---------------------------+---------+-----------+----------------------+---------------------------------------------------+
| IndexLookUp_8 | 0.00 | root | | |
| ├─Selection_7(Build) | 0.00 | cop[tikv] | | like(test.t1.a, "南", 92) |
| │ └─IndexRangeScan_5 | 0.00 | cop[tikv] | table:t1, index:a(a) | range:["SW","SW"], keep order:false, stats:pseudo |
| └─TableRowIDScan_6(Probe) | 0.00 | cop[tikv] | table:t1 | keep order:false, stats:pseudo |
+---------------------------+---------+-----------+----------------------+---------------------------------------------------+

[15:54:13]TiDB root:test> explain select * from t1 use index (a) where a = '南海';
+---------------------------+---------+-----------+----------------------+-----------------------------------------+
| id | estRows | task | access object | operator info |
+---------------------------+---------+-----------+----------------------+-----------------------------------------+
| IndexLookUp_7 | 1.00 | root | | |
| ├─IndexRangeScan_5(Build) | 1.00 | cop[tikv] | table:t1, index:a(a) | range:["SWmw","SWmw"], keep order:false |
| └─TableRowIDScan_6(Probe) | 1.00 | cop[tikv] | table:t1 | keep order:false |
+---------------------------+---------+-----------+----------------------+-----------------------------------------+
```
### 4. What is your TiDB version? (Required)
```sql
[15:50:20]TiDB root:test> select tidb_version();
+-----------------------------------------------------------+
| tidb_version() |
+-----------------------------------------------------------+
| Release Version: v7.6.0-alpha |
| Edition: Community |
| Git Commit Hash: 8fc13dadb250139694d608144219fb1ded041412 |
| Git Branch: heads/refs/tags/v7.6.0-alpha |
| UTC Build Time: 2023-12-07 02:50:32 |
| GoVersion: go1.21.4 |
| Race Enabled: false |
| Check Table Before Drop: false |
| Store: tikv |
+-----------------------------------------------------------+
```