LibWeb: Implement the "createLink" editing command

Author: https://github.com/gmta
Commit: 1b02e0dea3
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3216

Tests/LibWeb/Text/input/Editing/execCommand-createLink.html

@@ -0,0 +1,23 @@
+<script src="../include.js"></script>
+<div contenteditable="true" id="d1">foobar</div>
+<div contenteditable="true" id="d2"><a href="https://ladybird.dev">ladybird</a></div>
+<script>
+    test(() => {
+        const range = document.createRange();
+        getSelection().addRange(range);
+
+        // Make d1's 'bar' a link
+        const div1 = document.querySelector('#d1');
+        range.setStart(div1.childNodes[0], 3);
+        range.setEnd(div1.childNodes[0], 6);
+        document.execCommand('createLink', false, 'https://ladybird.org');
+        println(`d1 contents: "${div1.innerHTML}"`);
+
+        // Change d2's 'ladybird' href
+        const div2 = document.querySelector('#d2');
+        range.setStart(div2.childNodes[0].childNodes[0], 4);
+        range.setEnd(div2.childNodes[0].childNodes[0], 5);
+        document.execCommand('createLink', false, 'https://ladybird.org');
+        println(`d2 contents: "${div2.innerHTML}"`);
+    });
+</script>