Add Mono C# preprocessor testing to OS test demo

misc/os_test/MonoTest.cs

@@ -0,0 +1,93 @@
+using Godot;
+using System;
+
+public class MonoTest : Node
+{
+    public string Architecture()
+    {
+#if GODOT_ARM64 || GODOT_ARM64_V8A
+        return "64-bit ARM";
+#elif GODOT_ARMV7 || GODOT_ARMEABI_V7A
+        return "32-bit ARM";
+#elif GODOT_X86_64
+        return "64-bit x86";
+#elif GODOT_X86
+        return "32-bit x86";
+#elif GODOT_128
+        return "128-bit";
+#elif GODOT_64
+        return "64-bit";
+#elif GODOT_32
+        return "32-bit";
+#else
+        return "Unknown";
+#endif
+    }
+
+    public string OperatingSystem()
+    {
+#if GODOT_WINDOWS
+        return "Windows";
+#elif GODOT_LINUXBSD || GODOT_X11
+        return "Linux (or BSD)";
+#elif GODOT_SERVER
+        return "Server (Linux or BSD)";
+#elif GODOT_MACOS || GODOT_OSX
+        return "macOS";
+#elif GODOT_ANDROID
+        return "Android";
+#elif GODOT_IOS
+        return "iOS";
+#elif GODOT_HTML5
+        return "HTML5";
+#elif GODOT_HAIKU
+        return "Haiku";
+#elif GODOT_UWP
+        return "UWP (Windows 10)";
+#else
+        return "Unknown";
+#endif
+    }
+
+    public string PlatformType()
+    {
+#if GODOT_PC
+        return "PC";
+#elif GODOT_MOBILE
+        return "Mobile";
+#elif GODOT_WEB
+        return "Web";
+#elif GODOT
+        return "Godot Editor (not exported)";
+#else
+        return "Unknown";
+#endif
+    }
+
+    public string TextureCompression()
+    {
+        string compression = "";
+#if GODOT_S3TC
+        compression += "S3TC";
+#endif
+#if GODOT_ETC
+        if (compression.Length > 0)
+        {
+            compression += ", ";
+        }
+        compression += "ETC";
+#endif
+#if GODOT_ETC2
+        if (compression.Length > 0)
+        {
+            compression += ", ";
+        }
+        compression += "ETC2";
+#endif
+        if (compression.Length > 0)
+        {
+            return compression;
+        }
+        return "Not exported or no textures";
+    }
+}