redirect Console.Out to stderr

Redirecting Console.Out to use the standard error stream to try reduce
the chances of stdout being corrupted by non-rpc content.

src/LanguageServer/Microsoft.CodeAnalysis.LanguageServer/Program.cs

@@ -40,7 +40,19 @@
 
 static async Task RunAsync(ServerConfiguration serverConfiguration, CancellationToken cancellationToken)
 {
-    // Before we initialize the LSP server we can't send LSP log messages.
+    // Redirect Console.Out when using stdio to try prevent corruption of the LSP output
+    if (serverConfiguration.UseStdIo)
+    {
+        if (serverConfiguration.ServerPipeName is not null)
+        {
+            throw new Exception("Server cannot be started with both --stdio and --pipe options.");
+        }
+
+        // Redirect Console.Out to try prevent the standard output stream from being corrupted.
+        Console.SetOut(new StreamWriter(Console.OpenStandardError()));
+    }
+
+    // Before we initalize the LSP server we can't send LSP log messages.
     // Create a console logger as a fallback to use before the LSP server starts.
     using var loggerFactory = LoggerFactory.Create(builder =>
     {
@@ -246,7 +258,8 @@ static CliRootCommand CreateCommandLineParser()
     {
         Description = "Use stdio for communication with the client.",
         Required = false,
-        DefaultValueFactory = _ => false
+        DefaultValueFactory = _ => false,
+
     };
 
     var rootCommand = new CliRootCommand()