fix: 🐛 [JIRA: IOSSDKBUG-306] toolbar layout issue

[xiaoyu0722]

Use @StateObject to make sure the only true source of handler.

before	after

Test Code

#Preview {
    TestView()
}
class TestViewModel: ObservableObject {
    @Published var isScreenLoading = false
}
struct TestView: View {
    @StateObject var viewModel = TestViewModel()
    var body: some View {
        NavigationStack {
            Text("Hello world.")
                .fioriToolbar {
                    FioriButton { _ in
                        self.viewModel.isScreenLoading = true
                    } label: { _ in
                        Text("Change value")
                            .frame(maxWidth: .infinity)
                    }
                }
        }
    }
}