Feature: Support ANSI extension for ImGuiText

[ScottKane]

It would be really cool if we could get a port of one of the methods discussed here (https://github.com/ocornut/imgui/issues/902) for ImGui.NET. Not sure if this would be a pain if you are only DLLImporting functions from the cimgui dll, if there's any capacity to add bindings for this it would be great to have something like ImGui.TextAnsiUnformatted(ansiString)