(Breaking) DrawList: swapped the last two arguments of AddRect(), AddPolyline(), PathStroke(). thickness<>flags.

Added inline redirection functions when IMGUI_DISABLE_OBSOLETE_FUNCTIONS is off.
Marked the old functions are =delete when IMGUI_DISABLE_OBSOLETE_FUNCTIONS is on, to allow for better type-checking.
The aim is to be able to use/add flags to more ImDrawList functions, and making existing functions consistents was deemed very desirable.