Invoke (SendAsyncMethod) is lost when resizing window

[marius-klimantavicius]

Platform: windows (I am using this project as basis for supporting native AOT).

Steps to reproduce:

1. Create form
2. Add Load event handler:

Load += (_, _) => {
  ThreadPool.UnsafeQueueUserWorkItem(_ =>
  {
      Thread.Sleep(1000);
      for (var i = 0; i < 100; i++) {
  
          Invoke(() => _label.Text = $"Current: {i}");
          Thread.Sleep(300);
      }
  }, null);
};

3. Run app
4. Do resize

Expected result:
_label.Text is continuously updated

Actual result:
_label.Text stops being updated during and after resize

Reason:
This is because Invoke is handled by posting ASYNC_MESSAGE into message loop and expecting the message to be returned by GetMessage/PeekMessage. The issue is that when form is being resized it enters a resize message loop thus our calls to GetMessage/PeekMessage are "bypassed".

Possible fix.
Handle ASYNC_MESSAGE in WndProc instead of XplatUIWin32.GetMessage (this will also require the foster parent to have non-DefWndProc). This is what I have done locally.
Also consider using ASYNC_MESSAGE as a marker and store pending calls in a queue instead of actually sending call info via GCHandle (this is what dotnet/winforms does).

Also possible issue (not sure though): Control.GetInvokableHandle will call CreateHandle if handle does not exist. I am afraid that could cause the handle to be created on a wrong thread if Invoke is called before the control was created. But I don't know if that's a real issue or not I haven't encountered that (haven't tested it either).