Change SDL event handling to use pump/peep isntead of poll

As recommended in
libsdl-org/SDL#4794 (comment). Note
that the linked PR itself will also fix this without any changes our
side, but we will still get some extra efficiency by refactoring how we
are processing events regardless.

Should help with high poll rate input devices to some degree.

osu.Framework/Platform/SDL2DesktopWindow.cs

@@ -577,13 +577,23 @@ private void pollMouse()
 
         protected void ScheduleCommand(Action action) => commandScheduler.Add(action, false);
 
+        private const int events_per_peep = 64;
+        private SDL.SDL_Event[] events = new SDL.SDL_Event[events_per_peep];
+
         /// <summary>
         /// Poll for all pending events.
         /// </summary>
         private void pollSDLEvents()
         {
-            while (SDL.SDL_PollEvent(out var e) > 0)
-                handleSDLEvent(e);
+            SDL.SDL_PumpEvents();
+
+            int incoming;
+
+            while ((incoming = SDL.SDL_PeepEvents(events, events_per_peep, SDL.SDL_eventaction.SDL_GETEVENT, SDL.SDL_EventType.SDL_FIRSTEVENT, SDL.SDL_EventType.SDL_LASTEVENT)) > 0)
+            {
+                for (int i = 0; i < incoming; i++)
+                    handleSDLEvent(events[i]);
+            }
         }
 
         private void handleSDLEvent(SDL.SDL_Event e)