Examples: Initial ImGui 1.85 integration example. (#338)

* Examples: Initial ImGui 1.85 integration example.

* Attempt to load and compile shaders.

* ImGUI integration done with some workarounds.

* ImGUI integration: Cleanup example.

* refactor tests->example_imgui

Co-authored-by: Turánszki János <turanszkij@users.noreply.github.com>

Example_ImGui/stdafx.cpp

@@ -0,0 +1,8 @@
+// stdafx.cpp : source file that includes just the standard includes
+// $safeprojectname$.pch will be the pre-compiled header
+// stdafx.obj will contain the pre-compiled type information
+
+#include "stdafx.h"
+
+// TODO: reference any additional headers you need in STDAFX.H
+// and not in this file