feat: FileLogger. A small utility to log to a file identified by proc… (#481)

* feat: FileLogger. A small utility to log to a file identified by process ID. Useful when running multiple instances locally

Author: jeffreyrainy

com.unity.multiplayer.mlapi/Runtime/Logging/FileLogger.cs

@@ -0,0 +1,53 @@
+using System;
+using System.IO;
+
+#if DEVELOPMENT_BUILD || UNITY_EDITOR
+
+namespace MLAPI.Logging
+{
+    /// <summary>
+    /// Helper class for logging
+    /// Saves to a file identified by the current UTC epoch time. This is useful
+    /// when debugging what happens on multiple processes on the same machine
+    /// Only available for debugging on DEVELOPMENT_BUILD or UNITY_EDITOR
+    /// </summary>
+    public class FileLogger:IDisposable
+    {
+        private static FileLogger m_Instance = null;
+        public static FileLogger Instance
+        {
+            get
+            {
+                if (m_Instance == null)
+                {
+                    m_Instance = new FileLogger();
+                }
+                return m_Instance;
+            }
+        }
+
+        private StreamWriter m_Writer;
+
+        private FileLogger()
+        {
+            m_Writer = new StreamWriter("log." + DateTimeOffset.UtcNow.ToUnixTimeSeconds() + ".txt");
+            m_Writer.AutoFlush = true;
+        }
+
+        public void Dispose()
+        {
+            m_Writer.Dispose();
+        }
+
+        /// <summary>
+        /// Logs a line
+        /// <param name="line">The line to log to the file for this process</param>
+        /// </summary>
+        public void Log(string line)
+        {
+            m_Writer.WriteLine(line);
+        }
+    }
+}
+
+#endif