make `move_cursor_with_shift` public

[piscopancer]

It's impossible to create your own keymapping with selection bcs method responsible for that is not public

Input { key: Key::Right, ctrl: false, alt: true, .. } => {
  self.move_cursor_with_shift(CursorMove::WordForward); // function `move_cursor_with_shift` is private
  false
}