Rework Object's [[OwnPropertyKeys]] (#4001)

I've removed the ecma_op_object_get_property_names method, and implemented the following ones:
- ecma_op_object_own_property_keys: this is now the internal [[OwnPropertyKeys]] method
- ecma_op_object_enumerate: this is used for the for-in iterator
- ecma_object_sort_property_names: this is used for sorting the property names of an object
- ecma_object_list_lazy_property_names: this is for getting the lazy instantiated properties
- ecma_object_prop_name_is_duplicated: this is for checking if a given property is duplicated in an object

Also the for-in operation with Proxy object works with this patch, #3992 should be closed

JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

jerry-core/ecma/operations/ecma-proxy-object.h

@@ -92,9 +92,6 @@ ecma_value_t
 ecma_proxy_object_delete_property (ecma_object_t *obj_p,
                                    ecma_string_t *prop_name_p);
 
-ecma_value_t
-ecma_proxy_object_enumerate (ecma_object_t *obj_p);
-
 ecma_collection_t *
 ecma_proxy_object_own_property_keys (ecma_object_t *obj_p);