LibWeb: Handle overlapping floating box and left margin

Allow the left margin of a box which creates a block formatting context
to overlap with left floating boxes which are siblings in the document
tree.

Fixes #20233 and the comment layout on https://lobste.rs.

Tests/LibWeb/Layout/input/block-and-inline/block-with-hidden-overflow-after-sibling-float.html

@@ -0,0 +1,26 @@
+<style>
+    .a {
+        float: left;
+    }
+
+    .a4 {
+        display: block;
+    }
+
+    .c {
+        overflow: hidden;
+    }
+</style>
+
+<div>
+    <div>
+        <div class="a">
+            <div class="a4">AAAA</div>
+            <div>A</div>
+        </div>
+    </div>
+    <div style="margin-left: 100px">
+        <div>B</div>
+        <div class="c">C</div>
+    </div>
+</div>