Split Apple platform target and move platform state ownership

src/platform_legacy/legacy_platform_state.h

@@ -2,8 +2,52 @@
 
 #include "platform_api/platform_services.h"
 
+#if __LINUX__ || __WEB__
+struct GLFWwindow;
+#endif
+
+#if defined(__OBJC__) && defined(__IOS__)
+@class GameViewController;
+@class AppDelegate;
+#endif
+
+#if defined(__OBJC__) && defined(__OSX__)
+@class View;
+@class AppOSX;
+#endif
+
 namespace pp::platform::legacy {
 
+#if defined(__LINUX__) || defined(__WEB__)
+struct RetainedLegacyGlfwWindowHooks final {
+    std::function<void()> acquire_render_context;
+    std::function<void()> present_render_context;
+    std::function<void()> request_app_close;
+};
+
+struct RetainedLegacyGlfwWindowState final {
+    GLFWwindow* window = nullptr;
+    RetainedLegacyGlfwWindowHooks hooks;
+};
+
+[[nodiscard]] RetainedLegacyGlfwWindowState& active_legacy_glfw_window_state();
+[[nodiscard]] RetainedLegacyGlfwWindowHooks& active_legacy_glfw_window_hooks();
+#endif
+
+#if defined(__IOS__) || defined(__OSX__)
+struct RetainedLegacyAppleState final {
+#ifdef __IOS__
+    GameViewController* ios_view = nullptr;
+    AppDelegate* ios_app = nullptr;
+#elif defined(__OSX__)
+    View* osx_view = nullptr;
+    AppOSX* osx_app = nullptr;
+#endif
+};
+
+[[nodiscard]] RetainedLegacyAppleState& active_legacy_apple_state();
+#endif
+
 [[nodiscard]] const pp::platform::PlatformStoragePaths& active_legacy_storage_paths();
 
 }