SL-11910 [Win] Horizontal scroll

indra/llui/llscrollbar.cpp

indra/llui/llscrollbar.h

indra/llui/llscrollcontainer.cpp

indra/llui/llscrollcontainer.h

indra/llui/llscrolllistctrl.cpp

indra/llui/llscrolllistctrl.h

indra/llui/lltextbase.cpp

indra/llui/lltextbase.h

indra/llui/llview.cpp

indra/llui/llview.h

indra/llwindow/llmousehandler.h

indra/llwindow/llwindowcallbacks.cpp

indra/llwindow/llwindowcallbacks.h

indra/llwindow/llwindowwin32.cpp

indra/newview/llmediactrl.cpp

indra/newview/llmediactrl.h

indra/newview/lltool.cpp

indra/newview/lltool.h

indra/newview/lltoolpie.cpp

indra/newview/lltoolpie.h