Allow passing an input stream to use as stdin.

Certain cli programs will accept stdin as input and this enables that.

src/Faithlife.Build/AppRunner.cs

@@ -126,6 +126,7 @@ private static int DoRunApp(string path, AppRunnerSettings settings)
 
 		var handleOutputLine = settings.HandleOutputLine;
 		var handleErrorLine = settings.HandleErrorLine;
+		var inputStream = settings.InputStream;
 
 		var startInfo = new ProcessStartInfo
 		{
@@ -135,6 +136,7 @@ private static int DoRunApp(string path, AppRunnerSettings settings)
 			UseShellExecute = false,
 			RedirectStandardOutput = handleOutputLine is not null,
 			RedirectStandardError = handleErrorLine is not null,
+			RedirectStandardInput = inputStream is not null,
 			CreateNoWindow = false,
 		};
 
@@ -180,6 +182,14 @@ private static int DoRunApp(string path, AppRunnerSettings settings)
 
 		process.Start();
 
+		if (inputStream is not null)
+		{
+			using var reader = new StreamReader(inputStream);
+
+			process.StandardInput.Write(reader.ReadToEnd());
+			process.StandardInput.Close();
+		}
+
 		if (handleOutputLine is not null)
 			process.BeginOutputReadLine();
 

src/Faithlife.Build/AppRunnerSettings.cs

@@ -50,6 +50,11 @@ public sealed class AppRunnerSettings
 	/// </summary>
 	public Action<string>? HandleErrorLine { get; set; }
 
+	/// <summary>
+	/// If set, redirects standard in and uses this stream as input.
+	/// </summary>
+	public Stream? InputStream { get; set; }
+
 	/// <summary>
 	/// Clones the settings.
 	/// </summary>