Change ContentFactory.SERVICE.getInstance() to ContentFactory.getInstance() (flutter#6948) (flutter#6947)

See this for some additional context:
https://youtrack.jetbrains.com/issue/IDEA-299177/NoSuchMethodError-when-calling-com.intellij.ui.content.ContentFactory.getInstance

Author: jwren

flutter-idea/src/io/flutter/console/FlutterConsole.java

@@ -58,7 +58,7 @@ static FlutterConsole create(@NotNull Project project, @Nullable Module module)
     panel.setContent(view.getComponent());
 
     final String title = module != null ? "[" + module.getName() + "] Flutter" : "Flutter";
-    final Content content = ContentFactory.SERVICE.getInstance().createContent(panel.getComponent(), title, true);
+    final Content content = ContentFactory.getInstance().createContent(panel.getComponent(), title, true);
     Disposer.register(content, view);
 
     return new FlutterConsole(view, content, project, module);

flutter-idea/src/io/flutter/preview/PreviewView.java

@@ -186,7 +186,7 @@ public void loadState(@NotNull PreviewViewState state) {
   }
 
   public void initToolWindow(@NotNull ToolWindow toolWindow) {
-    final ContentFactory contentFactory = ContentFactory.SERVICE.getInstance();
+    final ContentFactory contentFactory = ContentFactory.getInstance();
     final ContentManager contentManager = toolWindow.getContentManager();
 
     final Content content = contentFactory.createContent(null, null, false);