update IWindowsFormsEditorService annotations

`IWindowsFormsEditorService.DropDownControl` now expects an non-null `Control` as argument

Author: halgab

src/System.Windows.Forms.Design/src/System/ComponentModel/Design/DesignerActionPanel.EditorPropertyLine.cs

@@ -418,9 +418,9 @@ void IWindowsFormsEditorService.CloseDropDown()
             CloseDropDown();
         }
 
-        void IWindowsFormsEditorService.DropDownControl(Control? control)
+        void IWindowsFormsEditorService.DropDownControl(Control control)
         {
-            ShowDropDown(control!, ActionPanel.BorderColor);
+            ShowDropDown(control, ActionPanel.BorderColor);
         }
 
         DialogResult IWindowsFormsEditorService.ShowDialog(Form dialog)

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

@@ -6539,7 +6539,7 @@ System.Windows.Forms.Design.IUIService.ShowToolWindow(System.Guid toolWindow) ->
 System.Windows.Forms.Design.IUIService.Styles.get -> System.Collections.IDictionary!
 System.Windows.Forms.Design.IWindowsFormsEditorService
 System.Windows.Forms.Design.IWindowsFormsEditorService.CloseDropDown() -> void
-System.Windows.Forms.Design.IWindowsFormsEditorService.DropDownControl(System.Windows.Forms.Control? control) -> void
+System.Windows.Forms.Design.IWindowsFormsEditorService.DropDownControl(System.Windows.Forms.Control! control) -> void
 System.Windows.Forms.Design.IWindowsFormsEditorService.ShowDialog(System.Windows.Forms.Form! dialog) -> System.Windows.Forms.DialogResult
 System.Windows.Forms.Design.PropertyTab
 System.Windows.Forms.Design.PropertyTab.~PropertyTab() -> void

src/System.Windows.Forms/src/System/Windows/Forms/Design/IWindowsFormsEditorService.cs

@@ -51,7 +51,7 @@ public interface IWindowsFormsEditorService
     ///   no other stored reference to the control.
     ///  </para>
     /// </remarks>
-    void DropDownControl(Control? control);
+    void DropDownControl(Control control);
 
     /// <summary>
     ///  Shows the specified <see cref="Form"/> as a dialog and returns its result. You should always use this