Refactor strategy determining the root annotation in a context

[DerManoMann]

Fixes #1226

This changes the way the code determines what is the root annotation in a context. The proposed new way is that an annotation is the root if:

• it is the only annotation
• it is the best match of being an instance or subclass of one of these classes (in priority order)
  • OA\Operation
  • OA\Property
  • OA\Parameter
    or (lowest priority) of type OpenApi\Annotations\Schemaor OpenApi\Attributes\Schema. In this case the exact class is required.