move core.twig_environment_render_template_after after environment->inject_assets

I'm writing my own little minifier to reduce page load, script size, and so on.

I tried to combine external css and js scripts, but some are injected after the core.twig_environment_render_template_after event, so that it is impossible to catch them.

It would be nice to have an event that fires after the total completition of template rendering.