LibWeb: Don't convert color functions to RGB when resolving color values

Author: https://github.com/tcl3
Commit: a97fe3123d
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4245
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/StyleValues/ColorFunctionStyleValue.h

@@ -21,6 +21,8 @@ public:
     virtual Color to_color(Optional<Layout::NodeWithStyle const&>) const override;
     virtual String to_string(SerializationMode) const override;
 
+    virtual bool is_color_function() const override { return true; }
+
     static constexpr Array s_supported_color_space = { "a98-rgb"sv, "display-p3"sv, "srgb"sv, "srgb-linear"sv, "prophoto-rgb"sv, "rec2020"sv, "xyz"sv, "xyz-d50"sv, "xyz-d65"sv };
 
 private: