Make the remote settings hook usable within the app extensions. (#4342)

ElementX/Sources/Application/Settings/RemotePreference.swift

@@ -0,0 +1,35 @@
+//
+// 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 Combine
+
+/// A setting that can be instantiated with a default value, remotely overridden and reset back
+/// to the default, automatically publishing the changes for downstream subscribers to react to.
+///
+/// Unlike ``UserPreference``, this type of setting isn't settable by the user, nor is the
+/// remote value persisted between app launches.
+struct RemotePreference<T: Equatable> {
+    private let defaultValue: T
+    private let subject: CurrentValueSubject<T, Never>
+    var publisher: CurrentValuePublisher<T, Never> { subject.asCurrentValuePublisher() }
+    var isRemotelyConfigured: Bool { subject.value != defaultValue }
+    
+    init(_ defaultValue: T) {
+        self.defaultValue = defaultValue
+        subject = .init(defaultValue)
+    }
+    
+    func applyRemoteValue(_ value: T) {
+        subject.send(value)
+    }
+    
+    func reset() {
+        if isRemotelyConfigured {
+            subject.send(defaultValue)
+        }
+    }
+}