Use PBM_SETMARQUEE to implement indeterminate mode in wxMSW wxGauge.

Use PBM_SETMARQUEE to implement indeterminate mode in wxMSW wxGauge.

The old code which simply used PBM_SETPOS after setting PBS_MARQUEE style
often worked but sometimes apparently didn't, so switch to the officially
sanctioned PBM_SETMARQUEE to implement this.

Also make wxGauge::SetDeterminateMode() and SetIndeterminateMode() methods
private as they are not part of the public class API.

Closes #11357.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64648 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775