LibWeb: Clamp calc()'d shadow blur radius to positive values

Author: https://github.com/Calme1709
Commit: 004bd3dc8f
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6208
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/Parser/Parser.h

@@ -551,6 +551,7 @@ private:
         DescriptorID descriptor;
     };
     enum SpecialContext : u8 {
+        ShadowBlurRadius,
         TranslateZArgument
     };
     using ValueParsingContext = Variant<PropertyID, FunctionContext, DescriptorContext, SpecialContext>;