LibWeb: Mostly implement ReadableByteStreamController.[[PullSteps]]

Author: https://github.com/mattco98
Commit: 51abecc8bc
Pull-request: https://github.com/SerenityOS/serenity/pull/18297
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/Streams/ReadableByteStreamController.h

@@ -117,6 +117,7 @@ public:
     void set_stream(JS::GCPtr<ReadableStream> stream) { m_stream = stream; }
 
     WebIDL::ExceptionOr<JS::GCPtr<WebIDL::Promise>> cancel_steps(JS::Value reason);
+    WebIDL::ExceptionOr<void> pull_steps(NonnullRefPtr<ReadRequest>);
 
 private:
     explicit ReadableByteStreamController(JS::Realm&);