Route render target binding through platform services

src/app.h

@@ -196,6 +196,8 @@ public:
     void acquire_render_context();
     void release_render_context();
     void present_render_context();
+    void bind_default_render_target();
+    void bind_main_render_target();
     void begin_render_capture_frame();
     void end_render_capture_frame();
     [[nodiscard]] bool platform_deletes_recorded_files_on_clear();