Speed up wxDataViewCtrl::SetSelections() on macOS

Don't make many single-item selection adjustments in SetSelections() in
wxOSX and instead implement it with a single native call to
selectRowIndexes:byExtendingSelection:

This has a dramatic, orders of magnitude effect on this call's
performance when selecting many items: selecting 10 thousand items goes
from minutes of runtime and gigabytes of RAM  to unobservable impact in
both.

include/wx/osx/cocoa/dataview.h

@@ -514,6 +514,7 @@ public:
     virtual int  GetSelections(wxDataViewItemArray& sel)   const;
     virtual bool IsSelected(const wxDataViewItem& item) const;
     virtual void Select(const wxDataViewItem& item);
+    virtual void Select(const wxDataViewItemArray& items);
     virtual void SelectAll();
     virtual void Unselect(const wxDataViewItem& item);
     virtual void UnselectAll();