fix(graph): #16904 introcuded percentage string here, such as '33%'. But it was based on canvas width/height, which is not reasonable - the unit may incorrect, and it is unpredictable if the `View['_rect']` is not calculated based on the current canvas rect. Therefore the percentage value is changed to based on `View['_rect'].width/height` since v6. Under this definition, users can use '0%' to map the top-left of `View['_rect']` to the center of `View['_viewRect']`.