Add recommended JSDoc tags

Many analysis tools will use JSDoc tags to determine what web component specific features. To keep from fragmenting the ecosystem around different sets of JSDoc, we should make a recommended set of tags.

Tags will need to document the features in the CustomElement schema kind:

- Tag Name
- Attributes
- Events
- Slots
- CSS Shadow Parts
- CSS Custom Properties
- Demos

Start with the CustomElement schema kind and compare its documented features with existing JSDoc conventions. Define a recommended tag set covering tag names, attributes, events, slots, CSS shadow parts, CSS custom properties, and demos; the issue names no files or tests, so completion requires agreement on the specification.

Written by the indexing model from the issue text.