[wpigui] Add wpigui wrappers for GLFW+imgui

These hide the platform specifics behind a common C++ API.  Platforms:
 - Windows: DirectX 11 (with 10 backwards compatibility)
 - Linux: OpenGL 3
 - Mac: Metal

shared/config.gradle

@@ -11,7 +11,7 @@ nativeUtils {
       niLibVersion = "2020.10.1"
       opencvVersion = "3.4.7-3"
       googleTestVersion = "1.9.0-4-437e100-1"
-      imguiVersion = "1.76-2"
+      imguiVersion = "1.76-6"
     }
   }
 }