js-on-sx: native prototypes inherit from Object.prototype

Per ES, every native prototype's [[Prototype]] is Object.prototype
(and Function.prototype.[[Prototype]] is too). Was missing those
links, so Object.prototype.isPrototypeOf(Boolean.prototype)
returned false (the explicit isPrototypeOf walks __proto__, not
the recent fallback). Added 5 dict-set! lines to the post-init.
built-ins/Boolean: 22/27 → 23/27, built-ins/Number: 44/50 → 45/50.
conformance.sh: 148/148.

lib/js/test262-scoreboard.json

@@ -40,6 +40,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 32.3,
+  "elapsed_seconds": 38.2,
   "workers": 1
 }