Always show channel toggle when collapsed (#3698)

This PR makes the channel toggle disclosure always visible when a
channel tree is collapsed, as opposed to just being visible on hover.

This makes it possible to visually identify collapsed channel trees
without having to hover over each entry.

Release Notes:

- N/A

crates/ui2/src/components/list/list_item.rs

@@ -192,7 +192,7 @@ impl RenderOnce for ListItem {
                             .flex()
                             .absolute()
                             .left(rems(-1.))
-                            .visible_on_hover("")
+                            .when(is_open, |this| this.visible_on_hover(""))
                             .child(Disclosure::new(is_open).on_toggle(self.on_toggle))
                     }))
                     .child(