LibWeb: Add a 'get a reader' helper method on ReadableStream

Author: https://github.com/shannonbooth
Commit: 9ce0c5914b
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3029
Reviewed-by: https://github.com/kennethmyhra ✅

Libraries/LibWeb/Streams/ReadableStream.h

@@ -105,6 +105,7 @@ public:
     State state() const { return m_state; }
     void set_state(State value) { m_state = value; }
 
+    WebIDL::ExceptionOr<GC::Ref<ReadableStreamDefaultReader>> get_a_reader();
     WebIDL::ExceptionOr<void> pull_from_bytes(ByteBuffer);
     WebIDL::ExceptionOr<void> enqueue(JS::Value chunk);
     void set_up_with_byte_reading_support(GC::Ptr<PullAlgorithm> = {}, GC::Ptr<CancelAlgorithm> = {}, double high_water_mark = 0);