implement onChanged

[AlexV525]

既可传controller也可使用onChanged，不强制要求使用controller来监听或控制行为。

/// The callback will execute field changed.
final ValueChanged<String> onChanged;
......
/// {@macro flutter.widgets.editableText.onChanged}
///
/// See also:
///
///  * [inputFormatters], which are called before [onChanged]
///    runs and can validate and change ("format") the input value.
///  * [onEditingComplete], [onSubmitted], [onSelectionChanged]:
///    which are more specialized input change notifications.
final ValueChanged<String> onChanged;

[TinoGuo]

It will be implemented in the next version.

[AlexV525]

Thanks. It helps a lot 👍

[TinoGuo]

implemented after bf7d1e3