trace2: add streamwriter

Add Trace2StreamWriter class which will be used to write to stderr or a
file, based on the TextWriter that is passed to it. It will also adapt the
output format based on the format target that is passed to it.

Author: Lessley Dennington

src/shared/Core/Trace2.cs

@@ -108,4 +108,6 @@ public abstract class Trace2Message
     public int Line { get; set; }
 
     public abstract string ToJson();
+
+    public abstract string ToNormalString();
 }

src/shared/Core/Trace2StreamWriter.cs

@@ -0,0 +1,65 @@
+using System;
+using System.IO;
+
+namespace GitCredentialManager;
+
+/// <summary>
+/// The different format targets supported in the TRACE2 tracing
+/// system.
+/// </summary>
+public enum Trace2FormatTarget
+{
+    Event,
+    Normal
+}
+
+public class Trace2StreamWriter : DisposableObject, ITrace2Writer
+{
+    private readonly TextWriter _writer;
+    private readonly Trace2FormatTarget _formatTarget;
+
+    public bool Failed { get; private set; }
+
+    public Trace2StreamWriter(TextWriter writer, Trace2FormatTarget formatTarget)
+    {
+        _writer = writer;
+        _formatTarget = formatTarget;
+    }
+
+    public void Write(Trace2Message message)
+    {
+        try
+        {
+            _writer.Write(Format(message));
+            _writer.Write('\n');
+            _writer.Flush();
+        }
+        catch
+        {
+            Failed = true;
+        }
+    }
+
+    protected override void ReleaseManagedResources()
+    {
+        _writer.Dispose();
+        base.ReleaseManagedResources();
+    }
+
+    private string Format(Trace2Message message)
+    {
+        EnsureArgument.NotNull(message, nameof(message));
+
+        switch (_formatTarget)
+        {
+            case Trace2FormatTarget.Event:
+                return message.ToJson();
+            case Trace2FormatTarget.Normal:
+                return message.ToNormalString();
+            default:
+                Console.WriteLine($"warning: unrecognized format target '{_formatTarget}', disabling TRACE2 tracing.");
+                Failed = true;
+                return "";
+        }
+    }
+}