Alex/disable onboarding existing users (#2105)

Task/Issue URL: https://app.asana.com/0/1177771139624306/1206416810557971/f

Description:
Disables onboarding for users having Data directory

DuckDuckGo/Application/AppDelegate.swift

@@ -102,6 +102,14 @@ final class AppDelegate: NSObject, NSApplicationDelegate, FileDownloadManagerDel
             fileStore = EncryptedFileStore()
         }
 
+        // keep this on top!
+        // disable onboarding for existing users
+        let isOnboardingFinished = UserDefaultsWrapper<Bool>(key: .onboardingFinished, defaultValue: false)
+        if !isOnboardingFinished.wrappedValue,
+           FileManager.default.fileExists(atPath: URL.sandboxApplicationSupportURL.path) {
+            isOnboardingFinished.wrappedValue = true
+        }
+
         let internalUserDeciderStore = InternalUserDeciderStore(fileStore: fileStore)
         internalUserDecider = DefaultInternalUserDecider(store: internalUserDeciderStore)
 

DuckDuckGo/Common/Utilities/UserDefaultsWrapper.swift

@@ -245,7 +245,7 @@ public struct UserDefaultsWrapper<T> {
 
             return value
         }
-        set {
+        nonmutating set {
             setValue(newValue)
         }
     }