docs(typescript): explain that virtuals inferred from schema only show up on Model, not raw document type

[vkarpov15]

Fix #12684

Summary

Documentation related to where virtuals show up with automatically inferred schema types, and why they show up where they do. Also how to get the hydrated doc type. Because we didn't have a good link to answer @Jokero 's questions in #12684

Examples

[hasezoey]

LGTM

[Jokero]

The problem with type UserDocument = ReturnType<(typeof UserModel)['hydrate']>; is that it returns Document type.
While it can be useful with normal (hydrated) queries, it won't work with lean option.

My current workaround is to manually extend the type returned by InferSchemaType:

type Point = InferSchemaType<typeof pointSchema> & {
    // virtual fields
    id: string;
    displayName: string;
}

And I can use this type with both normal (hydrated) and lean queries. This is what I wanted to report in #12684

[AbdelrahmanHafez]

LGTM, thanks! 👍

[vkarpov15]

@Jokero I presume you're using mongoose-lean-virtuals?

[Jokero]

@vkarpov15 yeah, I'm using it