message: [terminal] Selector: exposes selector mode.
diff: @@ -123,6 +123,8 @@ class Selector {
  return false;
  }
  + constexpr Mode mode() const noexcept { return mode_; }
  +
  /// Tests whether selection is upwards.
  constexpr bool negativeSelection() const noexcept { return to_ < from_; }
  constexpr bool singleLineSelection() const noexcept { return from_.row == to_.row; }
  