Seat: keep parent Xwayland view of a focused OR surface activated

Xwayland OR menus may disappear if their parent view is deactivated. The
heuristic and ICCCM input model implemented prior, used to determine whether an
OR surface may take focus, does not cover all menus, so retaining parent view
activation works as a catch-all solution for handling unwanted OR menu focus.

river/XwaylandView.zig

@@ -175,6 +175,16 @@ pub fn getConstraints(self: Self) View.Constraints {
 /// Called when the xwayland surface is destroyed
 fn handleDestroy(listener: *wl.Listener(*wlr.XwaylandSurface), _: *wlr.XwaylandSurface) void {
     const self = @fieldParentPtr(Self, "destroy", listener);
+    const view = self.view;
+
+    // Ensure no seat will attempt to access this view after it is destroyed.
+    var seat_it = server.input_manager.seats.first;
+    while (seat_it) |seat_node| : (seat_it = seat_node.next) {
+        const seat = &seat_node.data;
+        if (seat.activated_xwayland_view == view) {
+            seat.activated_xwayland_view = null;
+        }
+    }
 
     // Remove listeners that are active for the entire lifetime of the view
     self.destroy.link.remove();