This pull request introduces a new field named `helper` to the InputDecoration class. This field allows for specifying a widget containing contextual information about the InputDecorator.child's value. Unlike `helperText`, which accepts a plain string, `helper` supports widgets, enabling functionalities like tappable links for further explanation. This change aligns with the established pattern of `error`, `label`, `prefix`, and `suffix`.

fixes [#145163](https://github.com/flutter/flutter/issues/145163)