Delete keystroke

I tried to modify the Backspace function to simulate the delete key, it seems to work except for the first character. Does someone know if this feature has already been implemented in wip-input-widget?

```
func (self *TextBox) Delete() {
// ll: line length
if ll := len(self.text[self.cursorPoint.Y-1]); self.cursorPoint.X-1 < ll {
self.text[self.cursorPoint.Y-1] = append(self.text[self.cursorPoint.Y-1][:self.cursorPoint.X-1],
self.text[self.cursorPoint.Y-1][self.cursorPoint.X:]...)

}
}
```

Search the wip-input-widget for the TextBox.Delete method and the Backspace handling first. Compare the existing behavior around cursor positions, especially the first character, and check whether delete-key support already exists. Done means the delete keystroke behaves correctly at the cursor without removing the wrong character.

Written by the indexing model from the issue text.