Move Windows main task queue into platform services

src/platform_windows/windows_platform_services.cpp

@@ -22,11 +22,28 @@ void win32_save_window_state();
 bool win32_vr_start();
 void win32_vr_stop();
 HWND pp_windows_main_window_handle();
-void pp_windows_enqueue_main_task(std::packaged_task<void()> task);
 
 namespace pp::platform::windows {
 namespace {
 
+struct RetainedMainTaskQueue final {
+    std::deque<std::packaged_task<void()>> tasklist;
+    std::mutex task_mutex;
+};
+
+[[nodiscard]] RetainedMainTaskQueue& retained_main_task_queue()
+{
+    static RetainedMainTaskQueue queue;
+    return queue;
+}
+
+void enqueue_main_task(std::packaged_task<void()> task)
+{
+    auto& queue = retained_main_task_queue();
+    std::lock_guard<std::mutex> lock(queue.task_mutex);
+    queue.tasklist.emplace_back(std::move(task));
+}
+
 struct RetainedWin32AsyncRenderContextState final {
     HDC hdc{};
     HGLRC hrc{};
@@ -96,6 +113,27 @@ void swap_async_render_context()
 {
     SwapBuffers(retained_win32_async_render_context_state().hdc);
 }
+
+void enqueue_main_thread_task(std::packaged_task<void()> task)
+{
+    enqueue_main_task(std::move(task));
+}
+
+void drain_main_thread_tasks()
+{
+    std::deque<std::packaged_task<void()>> working_list;
+    {
+        auto& queue = retained_main_task_queue();
+        std::lock_guard<std::mutex> lock(queue.task_mutex);
+        working_list = std::move(queue.tasklist);
+    }
+
+    while (!working_list.empty())
+    {
+        working_list.front()();
+        working_list.pop_front();
+    }
+}
 } // namespace pp::platform::windows
 
 namespace {
@@ -159,7 +197,7 @@ void handle_gl_callback(
 
 void show_cursor(bool visible)
 {
-    pp_windows_enqueue_main_task(std::packaged_task<void()>([=] {
+    pp::platform::windows::enqueue_main_thread_task(std::packaged_task<void()>([=] {
         if (visible)
             while (ShowCursor(true) < 0);
         else