Add inferRawDocType helper

[vkarpov15]

Summary

As a potential workaround for #13772, this PR adds an inferRawDocType helper analogous to inferSchemaType (and mostly a copy of inferschematype.d.ts) to make it easier to automatically infer the raw doc type from the schema definition. This would also help with #13523. With this change, you can overwrite lean<> result types, etc.

Not ideal, but at least provides a workaround to more easily infer the correct raw doc type from the schema definition.

Examples

[vkarpov15]

Related issues: #12030

[hasezoey]

do i understand correctly that this type is for getting a POJO type from a schema definition type?

i dont really like to have to repeat similar code, but i guess this is necessary.

though is it really required that we re-define exact helper functions that (at least look to me) to be the same as in inferschematype?

[vkarpov15]

A lot of the helper types are identical, I will see if there's some way to fix that.

The reason why we need a similar helper function is because of how InferSchemaType is structured, there's no way to pass a UseHydratedDocument switch to InferSchemaType. The problem right now is that InferSchemaType doesn't quite return the fully hydrated document type or the raw document type, but something in-between. inferRawDocType is an attempt to return the raw doc type, which I think is a good first step in the right direction. We've tried some alternative approaches, like #13856, but it's proving tricky to work around the inherent restrictions with InferSchemaType.

[vkarpov15]

@hasezoey I found a way to reuse the helpers from inferschematypes 👍

[JavaScriptBach]

Isn't this just ObtainDocumentType? Or am I missing something?