Native: add KotlinThrowable.asError() to the generated Obj-C framework

This method can be useful when overriding a throwing Kotlin method in
Swift or Obj-C. In this case, a user can call asError to wrap Kotlin exception
to (NS)Error and then throw it to Kotlin, which will unwrap it back.

^KT-45127 Fixed

kotlin-native/runtime/src/main/cpp/ObjCExportErrors.h

@@ -6,4 +6,5 @@
 #import "Types.h"
 
 extern "C" id Kotlin_ObjCExport_ExceptionAsNSError(KRef exception, const TypeInfo** types);
+extern "C" id Kotlin_ObjCExport_WrapExceptionToNSError(KRef exception);
 extern "C" OBJ_GETTER(Kotlin_ObjCExport_NSErrorAsException, id error);

kotlin-native/runtime/src/main/cpp/ObjCExportErrors.mm

@@ -70,6 +70,10 @@ extern "C" id Kotlin_ObjCExport_ExceptionAsNSError(KRef exception, const TypeInf
     TerminateWithUnhandledException(exception);
   }
 
+  return Kotlin_ObjCExport_WrapExceptionToNSError(exception);
+}
+
+extern "C" id Kotlin_ObjCExport_WrapExceptionToNSError(KRef exception) {
   NSMutableDictionary<NSErrorUserInfoKey, id>* userInfo = [[NSMutableDictionary new] autorelease];
   userInfo[@"KotlinException"] = Kotlin_ObjCExport_refToObjC(exception);
   userInfo[@"KotlinExceptionOrigin"] = @(&kotlinExceptionOriginChar); // Support for different Kotlin runtimes loaded.