LibJS: Add AsyncFromSyncIteratorPrototype and Async-From-Sync instances

Until we have actual iterator records we have to store the sync iterator
as the raw object.

Userland/Libraries/LibJS/Forward.h

@@ -185,6 +185,7 @@ class ProxyConstructor;
 
 // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct constructor
 class GeneratorObjectPrototype;
+class AsyncFromSyncIteratorPrototype;
 
 class TypedArrayConstructor;
 class TypedArrayPrototype;