Got rid of API Compat warnings resulting from dotnet/csharplang#6065 :

src\System.Windows.Forms.Primitives\src\System\Windows\Forms\Message.cs#L31
src\System.Windows.Forms.Primitives\src\System\Windows\Forms\Message.cs(31,30): error RS0016: (NETCORE_ENGINEERING_TELEMETRY=Build) Symbol 'HWnd.get' is not part of the declared API.

src/System.Windows.Forms.Design/src/PublicAPI.Shipped.txt

@@ -949,10 +949,8 @@ System.Drawing.Design.ToolboxItem.ToolboxItem() -> void
 System.Drawing.Design.ToolboxItemCollection
 System.Drawing.Design.ToolboxItemCreatorCallback
 System.Runtime.InteropServices.UCOMITypeLib
-System.Runtime.InteropServices.UCOMITypeLib.GetLibAttr(out System.IntPtr ppTLibAttr) -> void
 System.Runtime.InteropServices.UCOMITypeLib.GetTypeInfoCount() -> int
 System.Runtime.InteropServices.UCOMITypeLib.GetTypeInfoType(int index, out System.Runtime.InteropServices.ComTypes.TYPEKIND pTKind) -> void
-System.Runtime.InteropServices.UCOMITypeLib.ReleaseTLibAttr(System.IntPtr pTLibAttr) -> void
 System.Windows.Forms.Design.AnchorEditor
 System.Windows.Forms.Design.AnchorEditor.AnchorEditor() -> void
 System.Windows.Forms.Design.AxImporter
@@ -986,7 +984,6 @@ System.Windows.Forms.Design.Behavior.BehaviorService.Dispose() -> void
 System.Windows.Forms.Design.Behavior.BehaviorService.EndDrag -> System.Windows.Forms.Design.Behavior.BehaviorDragDropEventHandler
 System.Windows.Forms.Design.Behavior.BehaviorService.Invalidate() -> void
 System.Windows.Forms.Design.Behavior.BehaviorService.Invalidate(System.Drawing.Rectangle rect) -> void
-System.Windows.Forms.Design.Behavior.BehaviorService.MapAdornerWindowPoint(System.IntPtr handle, System.Drawing.Point pt) -> System.Drawing.Point
 System.Windows.Forms.Design.Behavior.BehaviorService.ScreenToAdornerWindow(System.Drawing.Point p) -> System.Drawing.Point
 System.Windows.Forms.Design.Behavior.BehaviorService.Synchronize -> System.EventHandler
 System.Windows.Forms.Design.Behavior.BehaviorService.SyncSelection() -> void
@@ -1129,7 +1126,6 @@ System.Windows.Forms.Design.ThemedScrollbarMode.All = 1 -> System.Windows.Forms.
 System.Windows.Forms.Design.ThemedScrollbarMode.None = 2 -> System.Windows.Forms.Design.ThemedScrollbarMode
 System.Windows.Forms.Design.ThemedScrollbarMode.OnlyTopLevel = 3 -> System.Windows.Forms.Design.ThemedScrollbarMode
 System.Windows.Forms.Design.ThemedScrollbarWindow
-System.Windows.Forms.Design.ThemedScrollbarWindow.Handle -> System.IntPtr
 System.Windows.Forms.Design.ThemedScrollbarWindow.Mode -> System.Windows.Forms.Design.ThemedScrollbarMode
 System.Windows.Forms.Design.ThemedScrollbarWindow.ThemedScrollbarWindow() -> void
 System.Windows.Forms.Design.WindowsFormsDesignerOptionService

src/System.Windows.Forms.Design/src/PublicAPI.Unshipped.txt

@@ -0,0 +1,4 @@
+System.Runtime.InteropServices.UCOMITypeLib.GetLibAttr(out nint ppTLibAttr) -> void
+System.Runtime.InteropServices.UCOMITypeLib.ReleaseTLibAttr(nint pTLibAttr) -> void
+System.Windows.Forms.Design.Behavior.BehaviorService.MapAdornerWindowPoint(nint handle, System.Drawing.Point pt) -> System.Drawing.Point
+System.Windows.Forms.Design.ThemedScrollbarWindow.Handle -> nint

src/System.Windows.Forms.Primitives/src/PublicAPI.Shipped.txt

@@ -15,7 +15,6 @@ override System.Windows.Forms.PaddingConverter.GetCreateInstanceSupported(System
 override System.Windows.Forms.PaddingConverter.GetProperties(System.ComponentModel.ITypeDescriptorContext? context, object! value, System.Attribute![]? attributes) -> System.ComponentModel.PropertyDescriptorCollection!
 override System.Windows.Forms.PaddingConverter.GetPropertiesSupported(System.ComponentModel.ITypeDescriptorContext? context) -> bool
 static readonly System.Windows.Forms.Padding.Empty -> System.Windows.Forms.Padding
-static System.Windows.Forms.Message.Create(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam) -> System.Windows.Forms.Message
 static System.Windows.Forms.Message.operator !=(System.Windows.Forms.Message a, System.Windows.Forms.Message b) -> bool
 static System.Windows.Forms.Message.operator ==(System.Windows.Forms.Message a, System.Windows.Forms.Message b) -> bool
 static System.Windows.Forms.Padding.Add(System.Windows.Forms.Padding p1, System.Windows.Forms.Padding p2) -> System.Windows.Forms.Padding
@@ -63,16 +62,12 @@ System.Windows.Forms.HighDpiMode.SystemAware = 1 -> System.Windows.Forms.HighDpi
 System.Windows.Forms.Message
 System.Windows.Forms.Message.Equals(System.Windows.Forms.Message other) -> bool
 System.Windows.Forms.Message.GetLParam(System.Type! cls) -> object?
-System.Windows.Forms.Message.HWnd.get -> System.IntPtr
 System.Windows.Forms.Message.HWnd.set -> void
-System.Windows.Forms.Message.LParam.get -> System.IntPtr
 System.Windows.Forms.Message.LParam.set -> void
 System.Windows.Forms.Message.Message() -> void
 System.Windows.Forms.Message.Msg.get -> int
 System.Windows.Forms.Message.Msg.set -> void
-System.Windows.Forms.Message.Result.get -> System.IntPtr
 System.Windows.Forms.Message.Result.set -> void
-System.Windows.Forms.Message.WParam.get -> System.IntPtr
 System.Windows.Forms.Message.WParam.set -> void
 System.Windows.Forms.Padding
 System.Windows.Forms.Padding.All.get -> int

src/System.Windows.Forms.Primitives/src/PublicAPI.Unshipped.txt

@@ -0,0 +1,5 @@
+System.Windows.Forms.Message.HWnd.get -> nint
+System.Windows.Forms.Message.LParam.get -> nint
+System.Windows.Forms.Message.Result.get -> nint
+System.Windows.Forms.Message.WParam.get -> nint
+static System.Windows.Forms.Message.Create(nint hWnd, int msg, nint wparam, nint lparam) -> System.Windows.Forms.Message