Implement wxDataViewColumn::UnsetAsSortKey() in macOS version

It was impossible to stop sorting the control if it had been sorted
before, so implement UnsetAsSortKey() to allow doing it by destroying
the current sort descriptor.

Closes #18176.

docs/changes.txt

@@ -128,6 +128,7 @@ wxMSW:
 wxOSX:
 
 - Fix dispatching pending events (and CallAfter()) in console applications.
+- Implement wxDataViewColumn::UnsetAsSortKey() (Daniel Kulp).
 
 wxQt:
 

include/wx/osx/dataview.h

@@ -60,6 +60,7 @@ public:
     virtual void SetMinWidth   (int minWidth);
     virtual void SetReorderable(bool reorderable);
     virtual void SetResizeable (bool resizable);
+    virtual void UnsetAsSortKey();
     virtual void SetSortable   (bool sortable);
     virtual void SetSortOrder  (bool ascending);
     virtual void SetTitle      (wxString const& title);

src/osx/cocoa/dataview.mm

@@ -3465,6 +3465,13 @@ void wxDataViewColumn::SetResizeable(bool resizable)
         [m_NativeDataPtr->GetNativeColumnPtr() setResizingMask:NSTableColumnNoResizing];
 }
 
+void wxDataViewColumn::UnsetAsSortKey()
+{
+    NSTableColumn* const tableColumn = m_NativeDataPtr->GetNativeColumnPtr();
+    if ( tableColumn )
+        [tableColumn setSortDescriptorPrototype:nil];
+}
+
 void wxDataViewColumn::SetSortable(bool sortable)
 {
     // wxDataViewColumnBase::SetSortable(sortable);