Migrate recent HLLib work to BOS

It's better suited for the model of BOS and not an update to HLLibSharp

BurnOutSharp.Models/GCF/DirectoryLocalEntry.cs

@@ -0,0 +1,11 @@
+namespace BurnOutSharp.Models.GCF
+{
+    /// <see href="https://github.com/RavuAlHemio/hllib/blob/master/HLLib/GCFFile.h"/>
+    public sealed class DirectoryLocalEntry
+    {
+        /// <summary>
+        /// Index of the directory item.
+        /// </summary>
+        public uint DirectoryIndex;
+    }
+}