how to manual delete text with code for emoji

[zmtzawqlp]

Content

want to programmatically delete (backspace) a text input. and use manualDelete method.

if text contains emoji like 😃 👨‍👩‍👦 , it will throw substring does not support UTF-16. this is issue from dart dart-lang/sdk#35798

[zmtzawqlp]

done d7741ac