LibJS: Add spec comments to SymbolConstructor

Author: https://github.com/linusg
Commit: 0ae511edae
Pull-request: https://github.com/SerenityOS/serenity/pull/18336
Reviewed-by: https://github.com/trflynn89 ✅

Userland/Libraries/LibJS/Runtime/Symbol.h

@@ -24,6 +24,7 @@ public:
     bool is_global() const { return m_is_global; }
 
     ErrorOr<String> descriptive_string() const;
+    Optional<String> key() const;
 
 private:
     Symbol(Optional<String>, bool);