LibWeb: Add tests for flex formatting context

Author: https://github.com/kalenikaliaksandr
Commit: 92cb32b905
Pull-request: https://github.com/SerenityOS/serenity/pull/17365

Tests/LibWeb/Layout/input/flex-column-height-constrained-width-constrained.html

@@ -0,0 +1,24 @@
+<style>
+    body {
+        font-family: 'SerenitySans';
+    }
+
+    .container {
+        display: flex;
+        border: 1px solid salmon;
+        flex-direction: column;
+        height: 250px;
+        width: 250px;
+    }
+
+    .box {
+        width: 100px;
+        height: 100px;
+        border: 1px solid black;
+    }
+</style>
+<div class="container column">
+    <div class="box">1</div>
+    <div class="box">2</div>
+    <div class="box">3</div>
+</div>