Optimize generated code

[rolfbjarne]

There are numerous places where we can improve the generated code.

Example:

[MonoPInvokeCallback (typeof (DQLPreviewReplyDataCreationHandler))]
static unsafe IntPtr Invoke (IntPtr block, IntPtr reply, ref IntPtr error) {
    var descriptor = (BlockLiteral *) block;
    var del = (global::QuickLook.QLPreviewReplyDataCreationHandler) (descriptor->Target);
    var __xamarin_pref1 = Runtime.GetINativeObject<NSError> (error, false);
    Foundation.NSData retval = del ( Runtime.GetNSObject<QLPreviewReply> (reply), ref __xamarin_pref1);
    error = __xamarin_pref1 is null ? IntPtr.Zero : __xamarin_pref1.Handle;
    return retval.GetHandle ();
}

• Runtime.GetINativeObject<NSError> should be GetNSObject
• error = __xamarin_pref1 is null ? IntPtr.Zero : __xamarin_pref1.Handle; should be error = __xamarin_pref1.GetHandle ()`;

We should look at the generated code to find more opportunities.