Handles single and multiple sync failures

If a single sync failure is encountered a sheet is presented which allows the user to update their credentials.

If multiple sync failures are encountered an alert is shown listing the accounts which encountered errors. On iOS, this alert can take the user into Settings, but there is no obvious way to programatically pesent macOS preferences.

Multiplatform/Shared/SceneModel.swift

@@ -21,8 +21,8 @@ final class SceneModel: ObservableObject {
 	@Published var extractorButtonState: ArticleExtractorButtonState?
 	@Published var openInBrowserButtonState: Bool?
 	@Published var shareButtonState: Bool?
-
 	@Published var accountErrorMessage = ""
+	@Published var accountSyncErrors: [AccountSyncError] = []
 
 	var selectedArticles: [Article] {
 		timelineModel.selectedArticles
@@ -48,6 +48,7 @@ final class SceneModel: ObservableObject {
 		self.articleIconSchemeHandler = ArticleIconSchemeHandler(sceneModel: self)
 		self.webViewProvider = WebViewProvider(articleIconSchemeHandler: self.articleIconSchemeHandler!)
 
+		subscribeToAccountSyncErrors()
 		subscribeToToolbarChangeEvents()
 	}
 	
@@ -146,6 +147,16 @@ private extension SceneModel {
 		}.store(in: &cancellables)
 	}
 	
+	func subscribeToAccountSyncErrors() {
+		NotificationCenter.default.publisher(for: .AccountsDidFailToSyncWithErrors)
+			.sink { [weak self] notification in
+				guard let errors = notification.object as? [AccountSyncError] else {
+					return
+				}
+				self?.accountSyncErrors = errors
+			}.store(in: &cancellables)
+	}
+	
 	// MARK: Button State Updates
 	
 	func updateNextUnreadButtonState(accountManager: AccountManager) {