js-on-sx: bail out of array set/length at 2^32-1 instead of padding

arr[4294967295] = 'x' and arr.length = 4294967295 were padding
the SX list with js-undefined for ~4 billion entries — instant
timeout. Per ES spec, indices >= 2^32-1 aren't array indices
anyway (regular properties, which we can't store on lists).
Added (>= i 4294967295) bail clauses to js-list-set! and the
length setter.
built-ins/Array: 21/45 → 23/45 (5 timeouts → 2).
conformance.sh: 148/148.

lib/js/test262-scoreboard.json

@@ -1,35 +1,35 @@
 {
   "totals": {
-    "pass": 21,
-    "fail": 17,
+    "pass": 23,
+    "fail": 20,
     "skip": 5,
-    "timeout": 7,
+    "timeout": 2,
     "total": 50,
     "runnable": 45,
-    "pass_rate": 46.7
+    "pass_rate": 51.1
   },
   "categories": [
     {
       "category": "built-ins/Array",
       "total": 50,
-      "pass": 21,
-      "fail": 17,
+      "pass": 23,
+      "fail": 20,
       "skip": 5,
-      "timeout": 7,
-      "pass_rate": 46.7,
+      "timeout": 2,
+      "pass_rate": 51.1,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          14
-        ],
-        [
-          "Timeout",
-          7
+          17
         ],
         [
           "TypeError: not a function",
           2
         ],
+        [
+          "Timeout",
+          2
+        ],
         [
           "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
           1
@@ -40,22 +40,22 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      14
-    ],
-    [
-      "Timeout",
-      7
+      17
     ],
     [
       "TypeError: not a function",
       2
     ],
+    [
+      "Timeout",
+      2
+    ],
     [
       "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
       1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 123.5,
+  "elapsed_seconds": 51.3,
   "workers": 1
 }