The behavior of truncating when casting double as integer is not compatible with MySQL

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```
select cast(1.844674407370955e20 as unsigned);
```

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

```
mysql> select cast(1.844674407370955e20 as unsigned);
+----------------------------------------+
| cast(1.844674407370955e20 as unsigned) |
+----------------------------------------+
| 9223372036854775807 |
+----------------------------------------+
1 row in set (0.00 sec)

```

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

```
mysql> select cast(1.844674407370955e20 as unsigned int);
+--------------------------------------------+
| cast(1.844674407370955e20 as unsigned int) |
+--------------------------------------------+
| 18446744073709551615 |
+--------------------------------------------+
1 row in set, 1 warning (0.00 sec)

```

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