setInput method
Completely replaces the input content
Implementation
void setInput(String newText) {
final oldText = _tokenizer.getCurrentText();
if (oldText == newText) return;
// HLog.d(_tag, "替换内容, 新长度: ${newText.length}");
final edit = TextEdit.diff(oldText, newText);
_applyEdit(oldText.length, newText, edit);
}