[ddc] Cleanup type literals in JS() calls

One was an actual bug where an RTI was used when we wanted the
JavaScript class representing Dart Object class.

Issue: #46002
Change-Id: Ib5ece2578ff7421b6754258f95068a21ee55e055
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/415380
Reviewed-by: Mark Zhou <[email protected]>
Commit-Queue: Nicholas Shahan <[email protected]>

Author: nshahan

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/classes.dart

@@ -164,7 +164,7 @@ getGenericTypeCtor(value) => JS('', '#[#]', value, _genericTypeCtor);
 ///
 /// This is typically an instance's JS constructor.
 getTypeSignatureContainer(obj) {
-  if (obj == null) return JS('!', '#', Object);
+  if (obj == null) return JS_CLASS_REF(Object);
 
   // Object.create(null) produces a js object without a prototype.
   // In that case use the native Object constructor.

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart

@@ -732,7 +732,7 @@ bool dtest(obj) {
 asInt(obj) {
   // Note: null (and undefined) will fail this test.
   if (JS('!', 'Math.floor(#) != #', obj, obj)) {
-    castError(obj, JS('', '#', int));
+    castError(obj, TYPE_REF<int>());
   }
   return obj;
 }