Merge pull request #4870 from MarchingCube/fix-non-dwm-paint-handler-cycle

Revert change to win32 paint handler that was causing infinite repaints

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -343,16 +343,21 @@ namespace Avalonia.Win32
 
                 case WindowsMessage.WM_PAINT:
                 {
-                        using (_rendererLock.Lock())
+                    using (_rendererLock.Lock())
+                    {
+                        if (BeginPaint(_hwnd, out PAINTSTRUCT ps) != IntPtr.Zero)
                         {
-                            Paint?.Invoke(default);
+                            var f = RenderScaling;
+                            var r = ps.rcPaint;
+                            Paint?.Invoke(new Rect(r.left / f, r.top / f, (r.right - r.left) / f,
+                                (r.bottom - r.top) / f));
+                            EndPaint(_hwnd, ref ps);
                         }
-
-                        ValidateRect(hWnd, IntPtr.Zero);
-
-                        return IntPtr.Zero;
                     }
 
+                    return IntPtr.Zero;
+                }
+
                 case WindowsMessage.WM_SIZE:
                     {
                         using (_rendererLock.Lock())