LibWeb: Resolve CSS inset properties when entering inline-flow elements

We don't actually apply the insets anywhere yet, but at least now they
are available in the node's layout state.

Userland/Libraries/LibWeb/Layout/InlineLevelIterator.cpp

@@ -42,6 +42,9 @@ void InlineLevelIterator::enter_node_with_box_model_metrics(Layout::NodeWithStyl
     m_extra_leading_metrics->border += used_values.border_left;
     m_extra_leading_metrics->padding += used_values.padding_left;
 
+    // Now's our chance to resolve the inset properties for this node.
+    m_inline_formatting_context.compute_inset(node);
+
     m_box_model_node_stack.append(node);
 }