Add wxDataViewListCtrl::GetItemCount().

This method is convenient and (almost, except for the return value) compatible
with wxListCtrl.

See #11088.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71563 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datavcmn.cpp

@@ -1705,6 +1705,11 @@ unsigned int wxDataViewListStore::GetColumnCount() const
     return m_cols.GetCount();
 }
 
+unsigned int wxDataViewListStore::GetItemCount() const
+{
+    return m_data.size();
+}
+
 wxString wxDataViewListStore::GetColumnType( unsigned int pos ) const
 {
     return m_cols[pos];