LibJS: Remove Object(Object& prototype) footgun

This constructor was easily confused with a copy constructor, and it was
possible to accidentally copy-construct Objects in at least one way that
we dicovered (via generic ThrowCompletionOr construction).

This patch adds a mandatory ConstructWithPrototypeTag parameter to the
constructor to disambiguate it.

Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp

@@ -36,7 +36,7 @@ ThrowCompletionOr<NonnullGCPtr<GeneratorObject>> GeneratorObject::create(Realm&
 }
 
 GeneratorObject::GeneratorObject(Realm&, Object& prototype, ExecutionContext context)
-    : Object(prototype)
+    : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_execution_context(move(context))
 {
 }