Allow accepting a JSON substring using a string instead of throwing an exception

### Is your feature request related to a problem? Please describe.

no, this is my own need and idea.

### Describe the solution you'd like

such as json:
```json
{
"name": "root",
"child": {
"name": "child"
}
}
```

and i want to deserialize it into the following Java object:
```java
public class TestPojo {
private String name;
private String child;

// getter setter
}
```
I hope the deserialization can be successful, and the result of deserialization is:
name=root
child={"name":"child"}

### Usage example

```java
@Test
public void acceptSubJsonTest() throws Exception {
String json = "{\"name\":\"root\"," +
"\"child\":{\"name\":\"child\"}," +
"\"children\":[{\"name\":\"children\"}]," +
"\"childrenList\":[{\"name\":\"childrenList\"}]}";
ObjectMapper mapper = new ObjectMapper();
TestPojo testPojo = mapper.readValue(json, TestPojo.class);
Assertions.assertEquals(testPojo.getChild(), "{\"name\":\"child\"}");
Assertions.assertEquals(testPojo.getChildren(), "[{\"name\":\"children\"}]");
Assertions.assertEquals(testPojo.getChildrenList().get(0), "{\"name\":\"childrenList\"}");
}
```

### Additional context

I have submitted a PR to support this issue, please [click here](https://github.com/FasterXML/jackson-databind/pull/5232) to view.