LibWeb/CSS: Parse the ::slotted pseudo-element

Author: https://github.com/shannonbooth
Commit: 9054ff29f0
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5414
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/Dump.cpp

@@ -613,6 +613,7 @@ void dump_selector(StringBuilder& builder, CSS::Selector const& selector, int in
 
                 switch (pseudo_element_metadata.parameter_type) {
                 case CSS::PseudoElementMetadata::ParameterType::None:
+                case CSS::PseudoElementMetadata::ParameterType::CompoundSelector:
                     break;
                 case CSS::PseudoElementMetadata::ParameterType::PTNameSelector: {
                     auto const& [is_universal, value] = pseudo_element.pt_name_selector();