[BUG] Validator does not parse parameters if they are separated with anything but slash

Description

I have an API that contains the endpoint which looks like this:

"/api/processor/v1/designs/{id}/preview/{width}x{height}"

It looks like that the openapi-generator-cli does not support URLs that include parameters separated with a character that differs from '/'. When I try to validate it using openapi-generator-cli, it returns the following:

$ openapi-generator-cli validate -i processor.min.json
Validating spec (processor.min.json)
Errors:
        - attribute paths.'/api/processor/v1/designs/{id}/preview/{width}x{height}'. Declared path
          parameter width}x{height needs to be defined as a path parameter in path or operation
          level

[error] Spec has 1 errors.

Not sure whether the OpenAPI specification does allow this, but NSwag swallows it as well as the online validator at apidevtools.org. So I think it is a parser bug.

openapi-generator version

Both 4.3.1 and the latest one from docker (5.0.0-SNAPSHOT)

OpenAPI declaration file content or url

I have prepared a min repro:

---
openapi: 3.0.1
info:
  title: AssetProcessor API
  version: v1
paths:
  "/api/processor/v1/designs/{id}/preview/{width}x{height}":
    get:
      operationId: DesignProcessor_PreparePreview
      parameters:
      - name: id
        in: path
        required: true
        schema:
          type: string
          nullable: true
      - name: width
        in: path
        required: true
        schema:
          type: integer
          format: int32
      - name: height
        in: path
        required: true
        schema:
          type: integer
          format: int32
      responses:
        '200':
          description: Success

Steps to reproduce

Copy the above schema to a file named, say, schema.yml and run:

openapi-generator-cli validate -i schema.yml

Start with the schema.yml minimal reproduction and run openapi-generator-cli validate -i schema.yml. Trace validation of the path /api/processor/v1/designs/{id}/preview/{width}x{height} and confirm that width and height are recognized as separate path parameters; done means the command no longer reports them as an undefined combined parameter.