LibWeb: Extract MediaType to/from_string() logic into functions

Author: https://github.com/AtkinsSJ
Commit: 28278efafb
Pull-request: https://github.com/SerenityOS/serenity/pull/13824

Userland/Libraries/LibWeb/CSS/MediaQuery.h

@@ -258,6 +258,9 @@ String serialize_a_media_query_list(NonnullRefPtrVector<MediaQuery> const&);
 
 bool is_media_feature_name(StringView name);
 
+Optional<MediaQuery::MediaType> media_type_from_string(StringView);
+StringView to_string(MediaQuery::MediaType);
+
 }
 
 namespace AK {