Infer OpenApi parts from Method Based Operations

[kavics]

Generate OpenaApi elements from OData action/function methods.

• Use the base OpenApi document that defines metadata and elementary CRUD operations.
• Use references for complex parameters and response objects.
• Take care of object inheritances.
• Do not generate descriptions. Processing documentation will be a future issue.
• Overloads can be problematic: only parameter differences cannot be generated for OpenApi.
• Categorize operations by an attribute (e.g. [CategoryAttribute("ContentOperation")]). The codedoc element ///<SnCategory> is the wrong solution.
• Avoid empty object definitions in schemas. Generate new issues if needed.
• Normalize responses. For example, do not return HTTP 500 in case of a well-known error. Generate new issues if needed.