js-on-sx: ToPrimitive treats functions as non-primitive

Per ES, ToPrimitive only accepts strings/numbers/booleans/null
/undefined as primitives — objects AND functions trigger the next
step. Was treating function returns from toString/valueOf as
primitives (recursing to extract a string), so toString returning
a function didn't fall through to valueOf. Widened the dict-only
check to (or (= type "dict") (js-function? result)) in both
js-to-string and js-to-number ToPrimitive paths.
built-ins/String: 85/99 → 86/99. conformance.sh: 148/148.

lib/js/test262-scoreboard.json

@@ -1,61 +1,45 @@
 {
   "totals": {
-    "pass": 85,
-    "fail": 11,
-    "skip": 1,
-    "timeout": 3,
-    "total": 100,
-    "runnable": 99,
-    "pass_rate": 85.9
+    "pass": 46,
+    "fail": 2,
+    "skip": 0,
+    "timeout": 2,
+    "total": 50,
+    "runnable": 50,
+    "pass_rate": 92.0
   },
   "categories": [
     {
-      "category": "built-ins/String",
-      "total": 100,
-      "pass": 85,
-      "fail": 11,
-      "skip": 1,
-      "timeout": 3,
-      "pass_rate": 85.9,
+      "category": "built-ins/Number",
+      "total": 50,
+      "pass": 46,
+      "fail": 2,
+      "skip": 0,
+      "timeout": 2,
+      "pass_rate": 92.0,
       "top_failures": [
-        [
-          "Test262Error (assertion failed)",
-          9
-        ],
         [
           "Timeout",
-          3
+          2
         ],
         [
-          "ReferenceError (undefined symbol)",
-          1
-        ],
-        [
-          "SyntaxError (parse/unsupported syntax)",
-          1
+          "Test262Error (assertion failed)",
+          2
         ]
       ]
     }
   ],
   "top_failure_modes": [
-    [
-      "Test262Error (assertion failed)",
-      9
-    ],
     [
       "Timeout",
-      3
+      2
     ],
     [
-      "ReferenceError (undefined symbol)",
-      1
-    ],
-    [
-      "SyntaxError (parse/unsupported syntax)",
-      1
+      "Test262Error (assertion failed)",
+      2
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 182.4,
+  "elapsed_seconds": 71.0,
   "workers": 1
 }