Foreach API methods should not iterate over internal objects (#3537)

The `jerry_objects_foreach` and `jerry_objects_foreach_by_native_info` methods
iterates over all objects. However in ES 2015 there are a few special objects
which should only be used internally thus these objects should not be accessed
by the API user.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com

jerry-core/lit/lit-magic-strings.h

@@ -73,6 +73,7 @@ typedef enum
   LIT_INTERNAL_MAGIC_STRING_CLASS_THIS_BINDING, /**< the this binding of the class constructor */
   LIT_INTERNAL_MAGIC_STRING_WEAK_REFS, /**< Weak references to the current object */
   LIT_INTERNAL_MAGIC_STRING_CONTAINER, /**< Literal ID for internal container objects */
+  LIT_INTERNAL_MAGIC_STRING_INTERNAL_OBJECT, /**< Internal object ID for internal properties */
   LIT_MAGIC_STRING__COUNT /**< number of magic strings */
 } lit_magic_string_id_t;