Don't require AttributeProvider for JsonPropertyInfo-based modifications

[captainsafia]

This PR fixes a bug reported by @JamesNK in #56067.

Our OpenAPI implementation currently applies some transformations to the JSON schema produced by System.Text.Json in order to correctly produce $refs for nested types. The application of this fix was guarded behind a check that validated if the JsonPropertyInfo associated with the given schema had an AttributeProvider that we could query, although the AttributeProvider was not strictly needed for this check.

It turns out that for the case of types generated from protobuf-definitions, there's no implementation of IAtributeProvider resolved by System.Text.Json, so the fix was never applied for types used in a gRPC context.

To resolve this issue, we split up the check in TransformSchemaNode to only check for AttributeProvider when we strictly need it.

Below are the before/after for OpenAPI documents generated from the gRPC JsonTranscoding Sandbox app. Note the HelloReply schema.

Before

// 20240709182825
// https://localhost:5001/openapi/v1.json

{
  "openapi": "3.0.1",
  "info": {
    "title": "Sandbox | v1",
    "version": "1.0.0"
  },
  "paths": {
    "/v1/greeter/{name}": {
      "get": {
        "tags": [
          "Greeter"
        ],
        "parameters": [
          {
            "name": "name",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/HelloReply"
                }
              }
            }
          },
          "default": {
            "description": "",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Status"
                }
              }
            }
          }
        }
      }
    },
    "/v1/greeter": {
      "post": {
        "tags": [
          "Greeter"
        ],
        "requestBody": {
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/HelloRequestFrom"
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/HelloReply"
                }
              }
            }
          },
          "default": {
            "description": "",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Status"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "ArrayOfAny": {
        "type": "array",
        "nullable": true
      },
      "HelloReply": {
        "type": "object",
        "properties": {
          "message": {
            "type": "string"
          },
          "nested": {
            "$ref": "#/components/schemas/HelloReply2"
          }
        }
      },
      "HelloReply2": {
        "type": "object",
        "properties": {
          "message": {
            "type": "string"
          },
          "nested": {
            "$ref": "#/components/schemas/#/properties/nested"
          }
        },
        "nullable": true
      },
      "HelloRequestFrom": {
        "type": "object",
        "properties": {
          "name": {
            "type": "string"
          },
          "from": {
            "type": "string"
          }
        }
      },
      "Status": {
        "type": "object",
        "properties": {
          "code": {
            "type": "integer",
            "format": "int32",
            "nullable": true
          },
          "message": {
            "type": "string"
          },
          "details": {
            "$ref": "#/components/schemas/ArrayOfAny"
          }
        }
      }
    }
  },
  "tags": [
    {
      "name": "Greeter"
    }
  ]
}

After

// 20240709183500
// https://localhost:5001/openapi/v1.json

{
  "openapi": "3.0.1",
  "info": {
    "title": "Sandbox | v1",
    "version": "1.0.0"
  },
  "paths": {
    "/v1/greeter/{name}": {
      "get": {
        "tags": [
          "Greeter"
        ],
        "parameters": [
          {
            "name": "name",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/HelloReply"
                }
              }
            }
          },
          "default": {
            "description": "",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Status"
                }
              }
            }
          }
        }
      }
    },
    "/v1/greeter": {
      "post": {
        "tags": [
          "Greeter"
        ],
        "requestBody": {
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/HelloRequestFrom"
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/HelloReply"
                }
              }
            }
          },
          "default": {
            "description": "",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Status"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "ArrayOfAny": {
        "type": "array",
        "nullable": true
      },
      "HelloReply": {
        "type": "object",
        "properties": {
          "message": {
            "type": "string",
            "nullable": true
          },
          "nested": {
            "$ref": "#/components/schemas/HelloReply"
          }
        }
      },
      "HelloRequestFrom": {
        "type": "object",
        "properties": {
          "name": {
            "type": "string",
            "nullable": true
          },
          "from": {
            "type": "string",
            "nullable": true
          }
        }
      },
      "Status": {
        "type": "object",
        "properties": {
          "code": {
            "type": "integer",
            "format": "int32",
            "nullable": true
          },
          "message": {
            "type": "string",
            "nullable": true
          },
          "details": {
            "$ref": "#/components/schemas/ArrayOfAny"
          }
        }
      }
    }
  },
  "tags": [
    {
      "name": "Greeter"
    }
  ]
}

[JamesNK]

Consider adding a test.

But, assuming gRPC JSON transcoding relies on this, its tests will probably cover it.

[captainsafia]

But, assuming gRPC JSON transcoding relies on this, its tests will probably cover it.

This is the assumption that I was operating on. After a good night's rest though, I was able to figure out a way to simulate this scenario in tests here.