fix windows compilation warning
hide stl in the implementation instead of exporting it in the header to adress visual studio warning C4251 'needs to have dll-interface to be used by clients of the class'.
Backport: paraview/release
hide stl in the implementation instead of exporting it in the header to adress visual studio warning C4251 'needs to have dll-interface to be used by clients of the class'.
Backport: paraview/release