Fix panic with Narrator on Windows when transferring narrator focus

The action requests on Windows typically come in from a non-main thread,
so we'd try to clone the send wrapper in `do_action`
in a non-main thread. That panics unfortunately - send-wrapper
requires the clone to be done in the original thread.

To work around this, wrap the send-wrapper in an Arc, which we can
safely clone. Then inside the closure invoked from within the main thread,
we can clone the send wrapper safely and then take out the Weak
from it (safely as well).

internal/backends/winit/accesskit.rs

@@ -426,20 +426,24 @@ struct CachedNode {
 }
 
 struct ActionForwarder {
-    wrapped_window_adapter_weak: send_wrapper::SendWrapper<Weak<WinitWindowAdapter>>,
+    wrapped_window_adapter_weak: Arc<send_wrapper::SendWrapper<Weak<WinitWindowAdapter>>>,
 }
 
 impl ActionForwarder {
     pub fn new(window_adapter: &Weak<WinitWindowAdapter>) -> Self {
-        Self { wrapped_window_adapter_weak: send_wrapper::SendWrapper::new(window_adapter.clone()) }
+        Self {
+            wrapped_window_adapter_weak: Arc::new(send_wrapper::SendWrapper::new(
+                window_adapter.clone(),
+            )),
+        }
     }
 }
 
 impl accesskit::ActionHandler for ActionForwarder {
     fn do_action(&self, request: ActionRequest) {
         let wrapped_window_adapter_weak = self.wrapped_window_adapter_weak.clone();
         i_slint_core::api::invoke_from_event_loop(move || {
-            let Some(window_adapter) = wrapped_window_adapter_weak.take().upgrade() else { return };
+            let Some(window_adapter) = wrapped_window_adapter_weak.as_ref().clone().take().upgrade() else { return };
             window_adapter.accesskit_adapter.handle_request(request)
         })
         .ok();