LibWeb: Implement the "fontName" editing command

Author: https://github.com/gmta
Commit: 9366a50dd3
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3216

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

@@ -0,0 +1,22 @@
+<script src="../include.js"></script>
+<div contenteditable="true">foobar</div>
+<script>
+    test(() => {
+        const range = document.createRange();
+        getSelection().addRange(range);
+
+        const divElm = document.querySelector('div');
+
+        // Set fontName for 'bar'
+        range.setStart(divElm.childNodes[0], 3);
+        range.setEnd(divElm.childNodes[0], 6);
+        document.execCommand('fontName', false, 'monospace');
+        println(divElm.innerHTML);
+
+        // Set fontName for the entire editable div
+        range.setStart(divElm, 0);
+        range.setEnd(divElm, 2);
+        document.execCommand('fontName', false, 'sans-serif');
+        println(divElm.innerHTML);
+    });
+</script>