Add support for Swift objects inherited from objective-c classes

[anton-plebanovich]

Hi, I tried to use the Runtime and faced an issue with an object that inherits from the UIView. Property offsets were wrong. When I dug deeper I found that offsets don't count the instance size of UIView itself. I was able to workaround by modifying ClassMetadata's toTypeInfo() method like this:

mutating func toTypeInfo() -> TypeInfo {
    var info = TypeInfo(metadata: self)
    info.mangledName = mangledName()
    info.properties = properties()
    info.genericTypes = Array(genericArguments())

    var _sc: ClassMetadata? = self
    while var sc = _sc?.superClassMetadata()?.asClassMetadata() {
        info.inheritance.append(sc.type)
        let superInfo = sc.toTypeInfo()
        info.properties.append(contentsOf: superInfo.properties)
        _sc = sc
    }

    // Fix offset because of the obj-c inheritance if needed.
    // Fix own properties only.
    if let sc = _sc, let superClass = pointer.pointee.superClass as? AnyObject.Type {
        let size = class_getInstanceSize(superClass) - class_getInstanceSize(NSObject.self)
        for i in 0..<numberOfFields() {
            info.properties[i].offset += numericCast(size) // <--- I also made the offset writable to simplify things
        }
    }

    return info
}

I doubt it's the proper way of doing it and I was just curious If the issue can be fixed. Anyway, is it possible to add support for Swift objects inherited from objective-c classes?