Add a view with instructions for enabling backups in Element Classic. (#5359)

No presentation logic yet.

PreviewTests/Sources/GeneratedPreviewTests.swift

@@ -83,6 +83,14 @@ extension PreviewTests {
         }
     }
 
+    @Test
+    func authenticationClassicAppBackupInstructionsView() async throws {
+        AppSettings.resetAllSettings() // Ensure this test's previews start with fresh settings.
+        for (index, preview) in AuthenticationClassicAppBackupInstructionsView_Previews._allPreviews.enumerated() {
+            try await assertSnapshots(matching: preview, step: index)
+        }
+    }
+
     @Test
     func authenticationStartScreen() async throws {
         AppSettings.resetAllSettings() // Ensure this test's previews start with fresh settings.

PreviewTests/Sources/__Snapshots__/PreviewTests/authenticationClassicAppBackupInstructionsView.iPad-en-GB-0.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:1d033dd37f0c28c175f1181404ea9855963ffe830394dabfbbaf4877f36e52a4
+size 145715

PreviewTests/Sources/__Snapshots__/PreviewTests/authenticationClassicAppBackupInstructionsView.iPad-pseudo-0.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ffa8567fccd143f8dfe238c96d263717c99a6448953d3d10247b1012c751a956
+size 181186

PreviewTests/Sources/__Snapshots__/PreviewTests/authenticationClassicAppBackupInstructionsView.iPhone-en-GB-0.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:c20b19a79a4287aca05cc58d51e09232861361a5d9f29606f8a7eb912e78d2ee
+size 96938

PreviewTests/Sources/__Snapshots__/PreviewTests/authenticationClassicAppBackupInstructionsView.iPhone-pseudo-0.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ef97e734216be0e6ef36d0f0106c71728ea5a0cf57ce2164ad09157953dc22e2
+size 141919