Refactor EditorManager to utilize EditorSet for managing multiple editors per ROM, enhance ROM loading and saving processes, and improve popup management integration.

src/app/editor/editor.h

@@ -22,7 +22,7 @@ struct EditorContext {
   CommandManager command_manager;
   ExtensionManager extension_manager;
   HistoryManager history_manager;
-  PopupManager popup_manager;
+  PopupManager* popup_manager = nullptr;
   ShortcutManager shortcut_manager;
 };
 
@@ -76,6 +76,8 @@ class Editor {
 
   virtual absl::Status Find() = 0;
 
+  virtual absl::Status Clear() { return absl::OkStatus(); }
+
   EditorType type() const { return type_; }
 
   void set_context(EditorContext* context) { context_ = context; }