feat(lit-virtual): re-export the virtual-core public API - #1264

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: autofix-ci/action@551dded8c6cc8a1054039c8bc0b8b48c51dfc6ef. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/