Always display back button on catalyst

On iOS, you can dismiss modals by dragging down on them, or by tapping
outside of the modal. The same affordances are not made on MacOS. This
means that, if you open the contact details view on catalyst at the
moment, it is impossible to close the view, since we have disabled
showing the back button in AddTopLevelNavigation when the size class is
regular (which is normally the case on MacOS).

Therefore, if the current target is mac catalyst, we should always
display back buttons on modals, so that users can dismiss them without
having to force close the app.

Thanks lissine for finding this, and suggesting how to fix it.

Co-authored-by: lissine <[email protected]>

Monal/Classes/SwiftuiHelpers.swift

@@ -573,7 +573,11 @@ struct AddTopLevelNavigation<Content: View>: View {
                 .navigationBarTitleDisplayMode(.automatic)
                 .navigationBarBackButtonHidden(true) // will not be shown because swiftui does not know we navigated here from UIKit
                 .toolbar {
+#if targetEnvironment(macCatalyst)
+                    let shouldDisplayBackButton = true
+#else
                     let shouldDisplayBackButton = UIUserInterfaceSizeClass(rawValue: sizeClass.horizontal) == .compact
+#endif
                     if shouldDisplayBackButton {
                         ToolbarItem(placement: .topBarLeading) {
                             Button(action : {