[slots] @plone/slots first developments

Third level strategic package experiments

Experiments on the @plone/slots package. First trials on the shape as a not transpiled, not Volto add-on package to make it work-able as a node_modules package, and compatible with Next.js, vite-based frameworks and ultimately, Volto compatible too, just in case they are necessary there. In order to make it work, this kind of packages must not be under src directory. Let's not fight the ecosystem anymore in this matter. If the package is not being transpiled, the direct resolution must work OOTB, so the bundlers resolution is direct, and the TypeScript resolution too.

[ ] I signed and returned the Plone Contributor Agreement, and received and accepted an invitation to join a team in the Plone GitHub organization.
[ ] I verified there aren't other open pull requests for the same change.
[ ] I followed the guidelines in Contributing to Volto.
[ ] I succesfully ran code linting checks on my changes locally.
[ ] I succesfully ran unit tests on my changes locally.
[ ] I succesfully ran acceptance tests on my changes locally.
[ ] If needed, I added new tests for my changes.
[ ] If needed, I added documentation for my changes, either in the Storybook or narrative documentation.
[ ] I included a change log entry in my commits.

If your pull request closes an open issue, include the exact text below, immediately followed by the issue number. When your pull request gets merged, then that issue will close automatically.

Closes #

Name	Link
Latest commit	f47a8d0791c4daa9bf646d9ab055911f2463afa6
Latest deploy log	https://app.netlify.com/sites/plone-components/deploys/67438f8336c34600087acb3f

plone / volto