Support TResult | null for TypedDocumentNode when top-level data may be null

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

According to the GraphQL [specification](https://spec.graphql.org/October2021/#sel-DAPHEPHAAERBAAwyB), it's possible for the top-level data field in the response to be null in case of certain errors (e.g. when a non-nullable root field throws an unexpected error).

### Describe the solution you'd like

I’d like to have an option added to the `@graphql-codegen/typescript` plugin that allows it to generate TResult | null in operation result types.

graphql.ts
```ts:graphql.ts
export const GetHogeDocument = {
...
} as TypedDocumentNode
```

instead of the current:

```ts:graphql.ts
export const GetHogeDocument = {
...
} as TypedDocumentNode
```
This would allow safer and more accurate typing for clients where data: null is a valid result according to GraphQL spec.

### Describe alternatives you've considered

_No response_

### Any additional important details?

I asked the urql team about this, and they suggested handling it by altering the TypedDocumentNode type generated/produced.

Reference: https://github.com/urql-graphql/urql/issues/3803#issuecomment-3148608215