Refactor CoreCLR runtime into explicit dotnet api instead of mocking mono api

Required by platforms that will use mono under the hood for .Net 7
New `USE_CSHARP` define for C# ability
Engine doesn't use `mono_*` apis directly but via MCore/MClass/MMethod/ apis

Source/Engine/Scripting/Scripting.cs

@@ -4,6 +4,7 @@ using System;
 using System.Collections;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.InteropServices.Marshalling;
@@ -215,6 +216,11 @@ namespace FlaxEngine
             return ManagedHandle.Alloc(version);
         }
 
+        internal static ManagedHandle CultureInfoToManaged(int lcid)
+        {
+            return ManagedHandle.Alloc(new CultureInfo(lcid));
+        }
+
         internal static void VersionToNative(ManagedHandle versionHandle, IntPtr nativePtr)
         {
             Version version = Unsafe.As<Version>(versionHandle.Target);