[Swift 4] Property with type 'Any' does not conforms with codable protocol

Description

Current code generator for Swift 4 generates invalid code for JSON dictionaries or properties with object value type.

Property generated code:

open class TaskParameter: Codable {

    public var id: String?
    public var value: Any?

    public init() {}

}

Dictionary generated code:

open class EntityKey: Codable {
    public var entity: String?
    public var alias: String?
    public var fields: [String:Any]?

    public init() {}
} 

Swagger-codegen version

2.2.3

Swagger declaration file content or url

"definitions": {
"TaskParameter": {
            "type": "object",
            "properties": {
                "id": {
                    "type": "string"
                },
                "value": {
                    "type": "object"
                }
            }
        },
"EntityKey": {
            "type": "object",
            "properties": {
                "entity": {
                    "type": "string"
                },
                "alias": {
                    "type": "string"
                },
                "fields": {
                    "type": "object",
                    "additionalProperties": {
                        "type": "object"
                    }
                }
            }
        }
}

Command line used for generation

swagger-codegen generate -i ./swagger.json -l swift4 -o ./api

Steps to reproduce

Generate the code with swagger-codegen 2.2.3 then try to compile the generated classes on Xcode 9 GM or any beta version.

Related issues/PRs

Suggest a fix/enhancement

Seems like this problem relies on the fact that Any is not (and will be not) Codable, thus a generic "AnyCodable" that conforms to this protocol should be used instead.

StackOverflow Discussion
Apple Forum Discussion

Reproduce the issue with the supplied Swagger definition and the swagger-codegen generate -i ./swagger.json -l swift4 -o ./api command, then inspect the Swift 4 generator output for Codable properties and dictionaries typed as Any. Done means generated code for object-valued properties compiles under Xcode 9 and supports the reported JSON shapes.