Do this by removing the needs-update tracking. The gain was questionable to begin with and turns out it doesn't work correctly with multiple outputs.
Hide hidden workspaces by default, but add an option for overriding. While at it, move button visibility handling to Workspaces and only handle add/removal of buttons at WorkspaceManager. This makes it easier to keep track if sorting is needed.
The ext-workspace-v1 protocol is not wlr/wlroots specific.
