LibWeb: Move setting of Web object prototypes to initialize()

This needs to happen before prototype/constructor intitialization can be
made lazy. Otherwise, GC could run during the C++ constructor and try to
collect the object currently being created.

Userland/Libraries/LibWeb/Encoding/TextDecoder.h

@@ -35,6 +35,8 @@ private:
     // https://encoding.spec.whatwg.org/#dom-textdecoder
     TextDecoder(JS::Realm&, TextCodec::Decoder&, DeprecatedFlyString encoding, bool fatal, bool ignore_bom);
 
+    virtual void initialize(JS::Realm&) override;
+
     TextCodec::Decoder& m_decoder;
     DeprecatedFlyString m_encoding;
     bool m_fatal { false };