[BUG] Custom JsonMapper not working for RequestBody
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## Information

- **Version:** 7.29.1
- Packages:

I have a custom JsonMapper. This mapper is correctly used for `PathParams` but it is not used in `BodyParams`

## Example

```ts
// custom ID class
export class OrganizationId extends Id {
    public static PREFIX = 'OG'

    public getPrefix(): string {
        return OrganizationId.PREFIX;
    }
}

// JsonMapper
import { JsonMapper, JsonMapperCtx, JsonMapperMethods } from "@tsed/json-mapper";
import * as Ids from "@/ids";
import IdUtils from "@/ids/IdUtils";

@JsonMapper(...Object.values(Ids))
export class IdMapper implements JsonMapperMethods {
  deserialize<T extends Ids.Id>(data: any, ctx: JsonMapperCtx): T  {
    return IdUtils.fromHex(data);
  }

  serialize(id: Ids.Id): string {
    return id.getValue();
  }
}

// My protocol
import { UserId } from "@/ids";
import {Property, Required, Description} from "@tsed/schema";

export class AddUserToOrganizationRequest {
    @Property()
    @Required()
    @Description('The user id to add')
    userId: UserId;
}

// Controller method
@Post('/')
  @Returns(201, User)
  async create(@PathParams("organizationId") OrganizationId: OrganizationId, @BodyParams() body: AddUserToOrganizationRequest)
```

When I run this I get

```
{
  "name": "AJV_VALIDATION_ERROR",
  "message": "Bad request on parameter \"request.body\".\nAddUserToOrganizationRequest.userId must be object. Given value: \"US0d250728edf78ddcc9e4d5786bf86b00\"",
  "status": 400,
  "errors": [
    {
      "instancePath": "/userId",
      "schemaPath": "#/definitions/UserId/type",
      "keyword": "type",
      "params": {
        "type": "object"
      },
      "message": "must be object",
      "data": "US0d250728edf78ddcc9e4d5786bf86b00",
      "modelName": "AddUserToOrganizationRequest",
      "dataPath": ".userId"
    }
  ]
}
```

If I change the type to `string`, the everything works fine, including `OrganizationId` in the path parameter be in fact deserialized correctly. Why isn't this working for RequestBody?

## Acceptance criteria

- [ ] JsonMapper be used for request body as well
