Refactor window management and renderer integration for improved structure

- Replaced platform backend references with a dedicated Window class for better encapsulation of window and audio device management.
- Updated various files to include the new window header, enhancing clarity and reducing dependencies on the platform backend.
- Removed obsolete platform backend code to streamline the codebase and improve maintainability.
- Refactored controller and editor classes to utilize the new window management system, ensuring consistent handling of window creation and rendering.

src/app/editor/overworld/overworld_editor.cc

@@ -9,7 +9,7 @@
 #include "absl/strings/str_format.h"
 #include "app/core/features.h"
 #include "app/core/platform/clipboard.h"
-#include "app/core/platform/renderer.h"
+#include "app/core/window.h"
 #include "app/editor/graphics/palette_editor.h"
 #include "app/editor/overworld/entity.h"
 #include "app/gfx/arena.h"

src/app/editor/overworld/tile16_editor.cc

@@ -4,7 +4,7 @@
 
 #include "absl/status/status.h"
 #include "app/core/platform/file_dialog.h"
-#include "app/core/platform/renderer.h"
+#include "app/core/window.h"
 #include "app/gfx/bitmap.h"
 #include "app/gfx/snes_palette.h"
 #include "app/gui/canvas.h"