[js] Implement nqp::objectid.

Author: pmurias

src/vm/js/QAST/Compiler.nqp

@@ -1424,6 +1424,7 @@ class QAST::OperationsJS {
     add_simple_op('composetype', $T_OBJ, [$T_OBJ, $T_OBJ], :sideffects);
 
     add_simple_op('where', $T_INT, [$T_OBJ]);
+    add_simple_op('objectid', $T_INT, [$T_OBJ]);
 
     # HACK
     # TODO think what we should return on 1.WHAT and "foo".WHAT

src/vm/js/nqp-runtime/core.js

@@ -406,10 +406,11 @@ op.where = function(obj) {
     }
     return obj._WHERE;
   } else {
-    throw 'WHERE on this type of thing unimplemented';
+    throw 'WHERE/objectid on this type of thing unimplemented';
   }
 };
 
+op.objectid = op.where;
 
 /* HACK - take the current HLL settings into regard */