Keep members on the right sidebar, always

[Levi-Lesches]

I'm browsing the ChangeNotifier class.

I want to check out addListener and notifyListeners one after the other. In general, I cycle through member docs as I explore a class. The problem is, after clicking on any member on the right sidebar, the members list moves to the left side.

Proposal: Keep it on the right side, which is otherwise blank.

Alternative proposal: In line with #3437, move the members to the left side, replacing the "all classes in the library" list, which I agree with. It is way more common to cycle between elements of a class than classes in a library.