remove win32 dialog dpi hack (#18923)

Co-authored-by: Steven Kirk <grokys@users.noreply.github.com>

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

@@ -127,7 +127,6 @@ namespace Avalonia.Win32
                     }
 
                 case WindowsMessage.WM_DPICHANGED:
-                    if (!_ignoreDpiChanges)
                     {
                         _dpi = (uint)wParam >> 16;
                         var newDisplayRect = Marshal.PtrToStructure<RECT>(lParam);
@@ -149,19 +148,6 @@ namespace Avalonia.Win32
 
                         return IntPtr.Zero;
                     }
-                    else
-                    {
-                        // In case parent is on another screen with different scaling, window will have header scaled with
-                        // parent's scaling factor, so need to update frame
-                        SetWindowPos(hWnd,
-                            IntPtr.Zero, 0, 0, 0, 0,
-                            SetWindowPosFlags.SWP_FRAMECHANGED |
-                            SetWindowPosFlags.SWP_NOSIZE |
-                            SetWindowPosFlags.SWP_NOMOVE |
-                            SetWindowPosFlags.SWP_NOZORDER |
-                            SetWindowPosFlags.SWP_NOACTIVATE);
-                    }
-                    break;
 
                 case WindowsMessage.WM_GETICON:
                     if (_iconImpl == null)

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -104,7 +104,6 @@ namespace Avalonia.Win32
         private bool _shown;
         private bool _hiddenWindowIsParent;
         private uint _langid;
-        private bool _ignoreDpiChanges;
         internal bool _ignoreWmChar;
         private WindowTransparencyLevel _transparencyLevel;
         private readonly WindowTransparencyLevel _defaultTransparencyLevel;
@@ -730,20 +729,7 @@ namespace Avalonia.Win32
 
             _hiddenWindowIsParent = parentHwnd == OffscreenParentWindow.Handle;
 
-            // I can't find mention of this *anywhere* online, but it seems that setting
-            // GWL_HWNDPARENT to a window which is on the non-primary monitor can cause two
-            // WM_DPICHANGED messages to be sent: the first changing the DPI to the parent's DPI,
-            // then another changing the DPI back. This then causes Windows to provide an incorrect
-            // suggested new rectangle to the WM_DPICHANGED message if the window is immediately
-            // moved to the parent window's monitor (e.g. when using
-            // WindowStartupLocation.CenterOwner) causing the window to be shown with an incorrect
-            // size.
-            //
-            // Just ignore any WM_DPICHANGED while we're setting the parent as this shouldn't
-            // change the DPI anyway.
-            _ignoreDpiChanges = true;
             SetWindowLongPtr(_hwnd, (int)WindowLongParam.GWL_HWNDPARENT, parentHwnd);
-            _ignoreDpiChanges = false;
 
             // Windows doesn't seem to respect the HWND_TOPMOST flag of a window when showing an owned window for the first time.
             // So we set the HWND_TOPMOST again before the owned window is shown. This only needs to be done once.