Support Twig's CVA function

Problem/Motivation

Twig has a useful function for implementing CVA (Class Variance Authority). It's exposed by this small shim module: https://www.drupal.org/project/cva

The reasoning for exposing the function is well-explained on that project's page, so I won't repeat that here.

But it would benefit Drupal CMS, and theme developers generally, if we could just bring this function into core. It would require us to depend on twig/html-extra (at least to have the function consistently available, which is probably the best themer experience), but that appears to be, at a glance, maintained by the same folks who maintain Twig itself.

I propose we add twig/html-extra to core as a dependency, and make its functions available to Twig templates.

Dependency evaluation

This package is part of Twig -- it looks to be a subtree split: https://github.com/twigphp/Twig/blob/3.x/splitsh.json#L6

I think it's safe to assume that it therefore has the same maintainership, security policies, and release cycles as Twig itself, and I'm not sure that any further evaluation is necessary. It appears to release at the same time as Twig, at the same version.

Release notes snippet

Core now includes the twig/html-extra package, which exposes the html_cva, html_attr, and html_classes functions. All three are now available for use in Twig templates.