fix #336: NSProxy case - why WKWebView crashes on didReceiveAuthenticationChallenge

Follow up to issue #336: Could not find Java class corresponding to Objective-C class: WKNSURLAuthenticationChallenge.
Short story
WKWebView passes instance of internal/unexposed class WKNSURLAuthenticationChallenge as parameter instead of expected NSURLAuthenticationChallenge, and WKNSURLAuthenticationChallenge doesn’t extends from expected type.
Why it works? Because WKNSURLAuthenticationChallenge is NSProxy.

Long story
WKNSURLAuthenticationChallenge extends from WKObject which extends NSProxy. All these are not known by cocoa bindings so the crash is due it.
It works in obj-c side due nature of method invoking – through sending messages. And NSProxy provides ability to process any selector being sent to it instance. And WKNSURLAuthenticationChallenge handles all methods that to be provided by NSURLAuthenticationChallenge.

Solution
pushed as part of io12 bindings
NSProxy concept is not supported by RoboVM and compiler generate code that expects exact type match. This case solution is straight forward workaround:

• declare WKNSURLAuthenticationChallenge class to allow obj-c runtime to resolve it during marshaling;
• inherit it from NSURLAuthenticationChallenge to allows it apis to be called over WKNSURLAuthenticationChallenge instance.

@Library("WebKit") @NativeClass
public class WKNSURLAuthenticationChallenge extends NSURLAuthenticationChallenge {
}

Side effects
In long term this solution can be broken as WebKit can be updated and its logic changed. There might be following problems:

• logic of didReceiveAuthenticationChallenge is changed and WKNSURLAuthenticationChallenge is not passed there anymore;
• WKNSURLAuthenticationChallenge exposed as stand alone public class which makes name clash with workaround.

Bottom line
There is no common solution for NSProxy cases when binding. But approach is to substitute problematic class with surrogate class to fool runtime. It is good that NSProxy is usually internal objects and not exposes outside.