Avoid string allocations in MiniYaml parsing.

- Stream lines in as memory rather than needing to realise a string for each line, via a new method in StreamExts.
- Use span to avoid string allocations during parsing until we want to realise the node itself, in MiniYaml.FromLines.
- Change several callsites to use the streaming extension method rather than string method where possible.

OpenRA.Test/OpenRA.Game/StreamExtsTests.cs

@@ -0,0 +1,73 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2021 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System.IO;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+
+namespace OpenRA.Test
+{
+	[TestFixture]
+	class StreamExtsTests
+	{
+		[TestCase(TestName = "ReadAllLines is equivalent to ReadAllLinesAsMemory")]
+		public void ReadAllLines()
+		{
+			foreach (var source in new[]
+			{
+				"abc",
+				"abc\n",
+				"abc\r\n",
+				"abc\ndef",
+				"abc\r\ndef",
+				"abc\n\n\n",
+				"abc\r\n\r\n\r\n",
+				"abc\n\n\ndef",
+				"abc\r\n\r\n\r\ndef",
+				"abc\ndef\nghi\n",
+				"abc\r\ndef\r\nghi\r\n",
+				"abc\ndef\nghi\njkl",
+				"abc\r\ndef\r\nghi\r\njkl",
+				new string('a', 126),
+				new string('a', 126) + '\n',
+				new string('a', 126) + "\r\n",
+				new string('a', 126) + "b",
+				new string('a', 126) + "\nb",
+				new string('a', 126) + "\r\nb",
+				new string('a', 127),
+				new string('a', 127) + '\n',
+				new string('a', 127) + "\r\n",
+				new string('a', 127) + "b",
+				new string('a', 127) + "\nb",
+				new string('a', 127) + "\r\nb",
+				new string('a', 128),
+				new string('a', 128) + '\n',
+				new string('a', 128) + "\r\n",
+				new string('a', 128) + "b",
+				new string('a', 128) + "\nb",
+				new string('a', 128) + "\r\nb",
+				new string('a', 129),
+				new string('a', 129) + '\n',
+				new string('a', 129) + "\r\n",
+				new string('a', 129) + "b",
+				new string('a', 129) + "\nb",
+				new string('a', 129) + "\r\nb",
+			})
+			{
+				var bytes = Encoding.UTF8.GetBytes(source);
+				var lines = new MemoryStream(bytes).ReadAllLines().ToArray();
+				var linesAsMemory = new MemoryStream(bytes).ReadAllLinesAsMemory().Select(l => l.ToString()).ToArray();
+				Assert.That(linesAsMemory, Is.EquivalentTo(lines));
+			}
+		}
+	}
+}