LibJS: Add MarkedValueList and use it for argument passing

A MarkedValueList is basically a Vector<JS::Value> that registers with
the Heap and makes sure that the stored values don't get GC'd.

Before this change, we were unsafely keeping Vector<JS::Value> in some
places, which is out-of-reach for the live reference finding logic
since Vector puts its elements on the heap by default.

We now pass all the JavaScript tests even when running with "js -g",
which does a GC on every heap allocation.

Libraries/LibJS/Forward.h

@@ -63,6 +63,7 @@ class Heap;
 class HeapBlock;
 class Interpreter;
 class LexicalEnvironment;
+class MarkedValueList;
 class PrimitiveString;
 class ScopeNode;
 class Shape;