LibWeb: Forward media attribute from link element to loaded style sheet

Otherwise, we will treat the loaded style sheet as if it had media="all"
which is not always appropriate.

Tests/LibWeb/Text/input/link-element-media-attribute.html

@@ -0,0 +1,17 @@
+<style>
+body {
+    background: green;
+}
+</style>
+<script src="include.js"></script>
+<script>
+    let link = document.createElement("link");
+    link.setAttribute("rel", "stylesheet");
+    link.setAttribute("href", "body-background-color-red.css");
+    link.setAttribute("media", "print")
+    document.head.appendChild(link)
+
+    window.onload = function() {
+        println("document background: " + getComputedStyle(document.body).backgroundColor)
+    }
+</script>