Make the output of UnifiedDiffFormatter match diff -u

GNU 'diff -u' prefixes each line with either a space, a '+', or a '-'.
UnifiedDiffFormatter does the same, but it also adds an additional column of
whitespace between the prefix and the line. GNU diff only does that in
non-unified mode.

Fix this by implementing lines() in UnifiedDiffFormatter, overriding the parent
class implementation.

Bug: T100069
Change-Id: I1bf1b8e6d1d5aceb2c3836548f492f7edebe5a12

includes/diff/UnifiedDiffFormatter.php

@@ -36,6 +36,16 @@ class UnifiedDiffFormatter extends DiffFormatter {
 	/** @var int */
 	protected $trailingContextLines = 2;
 
+	/**
+	 * @param string[] $lines
+	 * @param string $prefix
+	 */
+	protected function lines( $lines, $prefix = ' ' ) {
+		foreach ( $lines as $line ) {
+			echo "{$prefix}{$line}\n";
+		}
+	}
+
 	/**
 	 * @param string[] $lines
 	 */