LibWeb: Implement WritableStream transfer

Author: https://github.com/trflynn89
Commit: cca08ad833
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4828
Reviewed-by: https://github.com/shannonbooth ✅

Libraries/LibWeb/HTML/StructuredSerialize.h

@@ -50,6 +50,7 @@ enum class TransferType : u8 {
     ArrayBuffer = 2,
     ResizableArrayBuffer = 3,
     ReadableStream = 4,
+    WritableStream = 5,
 };
 
 WebIDL::ExceptionOr<SerializationRecord> structured_serialize(JS::VM& vm, JS::Value);