Infer type from single allOf $ref

Specifying the description for a property with a complex type is not allowed; for example, this is invalid because the description will be wiped out by $ref replacement:

FooOperationURL:
    description: Endpoint that provides the ability to perform a foo operation
    type: string

preview_url:
    description: Endpoint at which to preview data
    $ref: '#/components/schemas/FooOperationURL

The suggested (messy & ugly, IMO) workaround for this is to specify the type in an allOf clause:

preview_url:
    description: Endpoint at which to preview data
    allOf:
        - $ref: '#/components/schemas/FooOperationURL

...but, ReDoc indicates that the type of preview_url in the latter case is merely string while in the former case it was much more usefully string (FooOperationURL).

I suggest that ReDoc treat a singular allOf $ref as the implied type of the property and therefore print that type hint in the documentation.

Start by tracing ReDoc's schema rendering for a property using a singular allOf entry with a $ref, using the examples in this issue as the input cases. Done means the generated documentation shows the referenced schema's type hint, such as string (FooOperationURL), while preserving the property's description.