Refactor DungeonEditor and related components for improved object management and UI enhancements

- Replaced vertical separators with standard separators in the EditorManager's menu bar for consistency.
- Introduced a new room selection callback mechanism in DungeonRoomSelector to facilitate room selection events.
- Enhanced DungeonEditor with drag-and-select functionality for object placement, improving user interaction.
- Added an object browser in DungeonObjectSelector for better object management and preview capabilities.
- Streamlined object rendering and selection processes, ensuring a more intuitive editing experience.

src/app/editor/dungeon/dungeon_object_selector.h

@@ -53,6 +53,7 @@ class DungeonObjectSelector {
 
  private:
   void DrawRoomGraphics();
+  void DrawObjectBrowser();
   void DrawCompactObjectEditor();
   void DrawCompactSpriteEditor();
   void DrawCompactItemEditor();