Migrate instances of EditorNotifications.Provider to the new API (-> interface of EditorNotificationProvider)

[jwren]

From the verify cli command:

      #Deprecated class com.intellij.ui.EditorNotifications.Provider reference
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.editor.NativeEditorNotificationProvider.<init>(Project)
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.samples.FlutterSampleNotificationProvider
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.inspections.SdkConfigurationNotificationProvider
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.editor.NativeEditorNotificationProvider
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.editor.FlutterPubspecNotificationProvider.<init>(Project)
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.inspections.SdkConfigurationNotificationProvider.<init>(Project)
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.editor.FlutterPubspecNotificationProvider
          Deprecated class com.intellij.ui.EditorNotifications.Provider is referenced in io.flutter.samples.FlutterSampleNotificationProvider.<init>(Project)