save the current status text for each pane inside wxStatusBarPane: native controls...

save the current status text for each pane inside wxStatusBarPane: native controls now store the (eventually) ellipsized version of the string; remove code for managing the status strings currently inside the [native|generic] control; add ellipsization support under wxMSW; now that all SetFieldsCount() implementation rrely on wxStatusBarBase::SetFieldsCount document how it behaves when adding new panes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58786 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775