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/core/dataview.h

@@ -90,6 +90,7 @@ public:
   virtual int  GetSelections(wxDataViewItemArray& sel)   const = 0; // returns all selected items in the native control
   virtual bool IsSelected   (wxDataViewItem const& item) const = 0; // checks if the passed item is selected in the native control
   virtual void Select       (wxDataViewItem const& item)       = 0; // selects the passed item in the native control
+  virtual void Select       (wxDataViewItemArray const& items) = 0; // selects the passed items in the native control
   virtual void SelectAll()                                     = 0; // selects all items in the native control
   virtual void Unselect     (wxDataViewItem const& item)       = 0; // unselects the passed item in the native control
   virtual void UnselectAll()                                   = 0; // unselects all items in the native control