Optimize OnPaint

[Lecrapouille]

On

void GDCef::RenderHandler::OnPaint(CefRefPtr<CefBrowser> browser, PaintElementType type,
                                   const RectList& dirtyRects, const void* buffer,
                                   int width, int height)

Converting buffer (CEF texture) to m_texture (Godot texture) implies multiple iteration on the whole texture before beeing stored.
Think how to optimize