Change three view buttons into one with menu arrow

Change three view buttons into one with menu arrow

Instead of showing three buttons, which is quite visually noisy, show
only one button that is split: First button, when clicked, loops
through the view modes. Second smaller button with the down arrow
shows menu of the available view modes.

See also
https://invent.kde.org/system/dolphin/-/issues/68#toolbar-button-changes

Alternative for https://invent.kde.org/system/dolphin/-/merge_requests/893

![Screencast_20250121_123718](/uploads/e8625c485c58a9c47e8168106b3e7419/Screencast_20250121_123718.mp4)