fix: make mongoose typings work without esmModuleInterop true

[Uzlopak]

Resolves #11664

[Uzlopak]

This was kind of messy Bug.

To get it work without esmModuleInterOp I had to move the imports into the namespace and do the default export in the namespace. Exporting a default forces you to explicitly export all types, interfaces,namespaces and classes in that specific namespace.

Moved NativeError and NativeDate out of the mongoose-namespace, as that was clearly wrong as we dont export such classes. Changed two "classes" (SchemaTypeOptions, MixedSchemaTypeOptions) to interfaces, as they can not be instantiated.

Fixed also validateSync typing and modified model.validate to properly handle pathsToValidate (normalized the behaviour).

[vkarpov15]

At first glance looks good. I'll do some quick tests this PR over the next couple of days.

[vkarpov15]

Thanks 👍