LibWeb: Implement calc() value equality check in a more efficient way

Instead of serializing two calc() values to String and then comparing
those strings, we can now compare calc() values by actually traversing
their internal CalculationNode tree.

This makes style recomputation faster on pages with lots of calc()
values since it's now much cheaper to check whether a property with
some calc() value actually changed.

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -6552,6 +6552,7 @@ public:
     {
         builder.appendff("{: >{}}UNPARSED({})\n", "", indent, m_component_value.to_debug_string());
     }
+    virtual bool equals(CalculationNode const&) const override { return false; }
 
 private:
     UnparsedCalculationNode(ComponentValue component_value)