MDL-55224 core: Import PHP-CSS-Parser into core

Part of MDL-55071

lib/php-css-parser/Value/Value.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Sabberworm\CSS\Value;
+
+use Sabberworm\CSS\Renderable;
+
+abstract class Value implements Renderable {
+    protected $iLineNo;
+
+    public function __construct($iLineNo = 0) {
+        $this->iLineNo = $iLineNo;
+    }
+    
+    /**
+     * @return int
+     */
+    public function getLineNo() {
+        return $this->iLineNo;
+    }
+
+    //Methods are commented out because re-declaring them here is a fatal error in PHP < 5.3.9
+	//public abstract function __toString();
+	//public abstract function render(\Sabberworm\CSS\OutputFormat $oOutputFormat);
+}