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/core/core.cmake

@@ -3,6 +3,7 @@ set(
   app/core/controller.cc
   app/emu/emulator.cc
   app/core/project.cc
+  app/core/window.cc
 )
 
 if (WIN32 OR MINGW OR UNIX AND NOT APPLE)