Menus: the wasm build has no unused import warning for menu_open

The only callers of `menus::menu_open` are the native palette-window
code in `panel_docking.rs` and its native tests, so on wasm32 the
re-export and the function were unused and `cargo xtask wasm` printed
two warnings for them. Both now carry `#[cfg(not(target_arch = "wasm32"))]`.
The menu bar still records whether a menu is open on every target.

crates/ui-egui/src/menus.rs

@@ -58,6 +58,7 @@ mod tree;
 mod ui_commands;
 
 pub use bar::menu_bar;
+#[cfg(not(target_arch = "wasm32"))]
 pub(crate) use bar::menu_open;
 pub(crate) use bar::{home_key, home_showing};
 #[cfg(test)]

crates/ui-egui/src/menus/bar.rs

@@ -68,6 +68,7 @@ fn menu_open_id() -> egui::Id {
 }
 
 /// Whether a menu of the in-window menu bar is open (`false` when no menu bar was drawn yet).
+#[cfg(not(target_arch = "wasm32"))]
 pub(crate) fn menu_open(ctx: &egui::Context) -> bool {
     ctx.data(|d| d.get_temp::<bool>(menu_open_id())).unwrap_or(false)
 }