js-on-sx: hoist var across nested blocks; var-decls become set!

JS var is function-scoped, but the transpiler only collected
top-level vars and re-emitted (define) everywhere; for-body var
shadowed the outer (un-hoisted) scope. Three-part fix:
1. js-collect-var-names recurses into js-block/js-for/js-while
   /js-do-while/js-if/js-try/js-switch/js-for-of-in;
2. var-kind decls emit (set! ...) instead of (define ...) since
   the binding is already created at function scope;
3. js-block uses js-transpile-stmt-list (no re-hoist) instead of
   js-transpile-stmts.
built-ins/Array: 17/45 → 18/45, String: 77/99 → 78/99.
conformance.sh: 148/148.

lib/js/test262-scoreboard.json

@@ -1,41 +1,37 @@
 {
   "totals": {
-    "pass": 17,
-    "fail": 21,
-    "skip": 5,
-    "timeout": 7,
-    "total": 50,
-    "runnable": 45,
-    "pass_rate": 37.8
+    "pass": 78,
+    "fail": 15,
+    "skip": 1,
+    "timeout": 6,
+    "total": 100,
+    "runnable": 99,
+    "pass_rate": 78.8
   },
   "categories": [
     {
-      "category": "built-ins/Array",
-      "total": 50,
-      "pass": 17,
-      "fail": 21,
-      "skip": 5,
-      "timeout": 7,
-      "pass_rate": 37.8,
+      "category": "built-ins/String",
+      "total": 100,
+      "pass": 78,
+      "fail": 15,
+      "skip": 1,
+      "timeout": 6,
+      "pass_rate": 78.8,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          16
+          13
         ],
         [
           "Timeout",
-          7
-        ],
-        [
-          "TypeError: not a function",
-          2
+          6
         ],
         [
           "ReferenceError (undefined symbol)",
-          2
+          1
         ],
         [
-          "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
+          "SyntaxError (parse/unsupported syntax)",
           1
         ]
       ]
@@ -44,26 +40,22 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      16
+      13
     ],
     [
       "Timeout",
-      7
-    ],
-    [
-      "TypeError: not a function",
-      2
+      6
     ],
     [
       "ReferenceError (undefined symbol)",
-      2
+      1
     ],
     [
-      "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
+      "SyntaxError (parse/unsupported syntax)",
       1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 151.1,
+  "elapsed_seconds": 224.9,
   "workers": 1
 }