[MPG][Diff] properties of SystemData is marked as readonly

[msyyc]

• SDK generated with typespec:
  

• SDK generated from swagger

[msyyc]

In swagger, SystemData is marked as "readonly" while its properties not, so SDK users can still set value for its properties. But typespec mark each property of its value as "readonly" so SDK users can't set value anymore. Although it is breaking, in view of that SystemData is usually only for deserialization, the difference shall not influence SDK users.

[allenjzhang]

@ArthurMa1978 , do we still need to keep this issue open?

[pshao25]

@mikekistler if the readonly flag is mark in a normal object, should it propagate to its properties? e.g.

 "arbitraryObject": {
      "type": "object",
      "readOnly": true,
      "properties": {
        "aproperty": {
          "type": "string",
          "description": "The identity that created the resource."
        }
    }
}

Is aproperty readonly?