LibWeb/WebGL+Meta: Stub getSupportedExtensions() and getExtension()

Author: https://github.com/kalenikaliaksandr
Commit: 7e78d7d332
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2688
Reviewed-by: https://github.com/ADKaster ✅

Libraries/LibWeb/WebGL/WebGLRenderingContext.h

@@ -39,6 +39,9 @@ public:
     void set_size(Gfx::IntSize const&);
     void reset_to_default_state();
 
+    Optional<Vector<String>> get_supported_extensions() const;
+    JS::Object* get_extension(String const& name);
+
 private:
     virtual void initialize(JS::Realm&) override;