Called when the user submits editable content (e.g., user presses the "done" button on the keyboard).
The default implementation of onEditingComplete executes 2 different behaviors based on the situation:
When a completion action is pressed, such as "done", "go", "send", or "search", the user's content is submitted to the controller and then focus is given up.
When a non-completion action is pressed, such as "next" or "previous", the user's content is submitted to the controller, but focus is not given up because developers may want to immediately move focus to another input widget within onSubmitted.
Providing onEditingComplete prevents the aforementioned default behavior.
final VoidCallback onEditingComplete