LibWeb: Add HTMLPreElement width property

Author: https://github.com/bplaat
Commit: https://github.com/SerenityOS/serenity/commit/089a98607c
Pull-request: https://github.com/SerenityOS/serenity/pull/23261
Reviewed-by: https://github.com/ADKaster ✅

Tests/LibWeb/Text/input/HTML/pre-width.html

@@ -0,0 +1,29 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let testCounter = 1;
+        function testPart(part) {
+            println(`${testCounter++}. ${JSON.stringify(part())}`);
+        }
+
+        // 1. Set the pre element width attributes
+        testPart(() => {
+            const pre = document.createElement('pre');
+            pre.width = 20;
+            return pre.width;
+        });
+
+        // 2. Set the pre element width attributes with invalid data
+        testPart(() => {
+            const pre = document.createElement('pre');
+            pre.width = 'dsafds';
+            return pre.width;
+        });
+
+        // 3. Get the pre element width attribute default value
+        testPart(() => {
+            const pre = document.createElement('pre');
+            return pre.width;
+        });
+    });
+</script>