Improve positioning of wxSlider min/max labels in wxMSW.

Put the min/max labels on the sides or a horizontal slider or above/below a
vertical one to make them visually more distinct from the current value label.

See #11427.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65941 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775