Add a Webcomponent Manifest

[jogibear9988]

I've a Designer Framework for webcomponents: https://node-projects.github.io/web-component-designer-demo/index.html

It could use external NPM packages, but depends that they have a webcomponent manifest (see: https://github.com/webcomponents/custom-elements-manifest).
Would it be possible to add one to the npm package?

[jogibear9988]

for example see: the shoelace elemnts could be used directly

[break-stuff]

This would also be really helpful to add framework and IDE integrations to the project.

[asyncLiz]

Duplicate of #545, we'll track it there