message: Fix live right-click expansion
  While the commit introduced
  right click as a way to expand the active selection, it did not allow
  for holding right click to continuously do so.
  This commit remedies that problem by allowing live expansion with while
  holding the right mouse button.
diff: @@ -361,7 +361,9 @@ impl<'a, T: EventListener, A: ActionContext<T>> Processor<'a, T, A> {
  self.ctx.window_mut().set_mouse_cursor(mouse_state.into());
  let last_term_line = self.ctx.terminal().grid().num_lines() - 1;
  - if lmb_pressed && (self.ctx.modifiers().shift() || !self.ctx.mouse_mode()) {
  + if (lmb_pressed || self.ctx.mouse().right_button_state == ElementState::Pressed)
  + && (self.ctx.modifiers().shift() || !self.ctx.mouse_mode())
  + {
  // Treat motion over message bar like motion over the last line.
  let line = min(point.line, last_term_line);
  @@ -558,6 +560,11 @@ impl<'a, T: EventListener, A: ActionContext<T>> Processor<'a, T, A> {
  selection.ty = selection_type;
  self.ctx.update_selection(point, cell_side);
  +
  + // Move vi mode cursor to mouse click position.
  + if self.ctx.terminal().mode().contains(TermMode::VI) {
  + self.ctx.terminal_mut().vi_mode_cursor.point = point;
  + }
  }
  /// Handle left click selection and vi mode cursor movement.
  @@ -589,9 +596,8 @@ impl<'a, T: EventListener, A: ActionContext<T>> Processor<'a, T, A> {
  ClickState::None => (),
  };
  - // Move vi mode cursor to mouse position.
  + // Move vi mode cursor to mouse click position.
  if self.ctx.terminal().mode().contains(TermMode::VI) {
  - // Update Vi mode cursor position on click.
  self.ctx.terminal_mut().vi_mode_cursor.point = point;
  }
  }
  