LibWeb/WebGL: Implement drawingBufferWidth and drawingBufferHeight

Author: https://github.com/kalenikaliaksandr
Commit: c199be061a
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2878
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/gmta

Libraries/LibWeb/WebGL/WebGLRenderingContext.h

@@ -43,6 +43,9 @@ public:
     Optional<Vector<String>> get_supported_extensions() const;
     JS::Object* get_extension(String const& name);
 
+    WebIDL::Long drawing_buffer_width() const;
+    WebIDL::Long drawing_buffer_height() const;
+
 private:
     virtual void initialize(JS::Realm&) override;