path parameters in $refs are not picked up

given

main.yml:
```
paths:
/my/{path}/somewhere:
$ref: external.yml#/~1my~1{path}~1somewhere
```

external.yml:

```
/my/{path}/somewhere:
parameters:
- in: path
name: path
required: true
get:
operationId: myExternalOp
resonses:
'200':
description: ok
```

no route parameter for path is created in the handler interface

Reproduce the issue using the main.yml and external.yml examples, then trace how the referenced path is processed into the generated handler interface. Done means the path parameter is present in that interface for the external $ref case, with the existing generation checks passing.

Written by the indexing model from the issue text.