LibJS: Parse async generator functions

Author: https://github.com/davidot
Commit: 0982a73d1d
Pull-request: https://github.com/SerenityOS/serenity/pull/10926
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/FunctionKind.h

@@ -12,6 +12,7 @@ enum class FunctionKind {
     Generator,
     Regular,
     Async,
+    AsyncGenerator
 };
 
 }