SL-16330 Clean up vertical sync handling, add to UI

indra/llwindow/llwindow.cpp

indra/llwindow/llwindow.h

indra/llwindow/llwindowheadless.cpp

indra/llwindow/llwindowheadless.h

indra/llwindow/llwindowmacosx.cpp

indra/llwindow/llwindowmacosx.h

indra/llwindow/llwindowwin32.cpp

indra/llwindow/llwindowwin32.h

indra/newview/app_settings/settings.xml

indra/newview/llviewercontrol.cpp

indra/newview/llviewerwindow.cpp

indra/newview/llviewerwindow.h

indra/newview/pipeline.cpp

.../default/xui/en/floater_preferences_graphics_advanced.xml