Joining a space from the room flow. (#4563)

* Add the More menu to SpaceScreen.

And a simple way to leave a space for testing.

* Start a space flow when accepting a space invite from the room flow.

* Minimise the tab bar on iOS 26 when scrolling down.

* Enable spaces by default!

ElementX/Sources/Other/SwiftUI/Backports.swift

@@ -0,0 +1,19 @@
+//
+// Copyright 2025 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+// Please see LICENSE files in the repository root for full details.
+//
+
+import SwiftUI
+
+extension View {
+    @ViewBuilder
+    func backportTabBarMinimizeBehaviorOnScrollDown() -> some View {
+        if #available(iOS 26.0, *) {
+            tabBarMinimizeBehavior(.onScrollDown)
+        } else {
+            self
+        }
+    }
+}