LibWeb/WebGL: Implement getSupportedExtensions()

Author: https://github.com/kalenikaliaksandr
Commit: 145bb0f849
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2878
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/gmta

Libraries/LibWeb/WebGL/OpenGLContext.h

@@ -30,6 +30,8 @@ public:
 
     RefPtr<Gfx::PaintingSurface> surface();
 
+    Vector<String> get_supported_extensions();
+
 private:
     NonnullRefPtr<Gfx::SkiaBackendContext> m_skia_backend_context;
     Gfx::IntSize m_size;