refactor: make instance non-nullable

Author: russellwheatley

FirebaseSwiftUI/FirebaseFacebookSwiftUI/Sources/Services/AuthService+Facebook.swift

@@ -10,7 +10,7 @@ import FirebaseAuthSwiftUI
 public extension AuthService {
   @discardableResult
   func withFacebookSignIn(scopes scopes: [String]? = nil) -> AuthService {
-    FacebookProviderAuthUI.configureSharedInstance(scopes: scopes)
+    FacebookProviderAuthUI.configureProvider(scopes: scopes)
     register(provider: FacebookProviderAuthUI.shared)
     return self
   }

FirebaseSwiftUI/FirebaseFacebookSwiftUI/Sources/Services/FacebookProviderAuthUI.swift

@@ -27,16 +27,14 @@ public class FacebookProviderAuthUI: FacebookProviderAuthUIProtocol {
   // Needed for reauthentication
   var isLimitedLogin: Bool = true
 
-  @MainActor private static var _shared: FacebookProviderAuthUI?
+  @MainActor private static var _shared: FacebookProviderAuthUI =
+    .init(scopes: kDefaultFacebookScopes)
 
   @MainActor public static var shared: FacebookProviderAuthUI {
-    guard let instance = _shared else {
-      fatalError("`FacebookProviderAuthUI` has not been configured")
-    }
-    return instance
+    return _shared
   }
 
-  @MainActor public static func configureSharedInstance(scopes: [String]? = nil) {
+  @MainActor public static func configureProvider(scopes: [String]? = nil) {
     _shared = FacebookProviderAuthUI(scopes: scopes)
   }