[css-paint-api] lack of complete examples is problematic

[dbaron]

One thing that I think all three of the TAG members who looked at the paint-api specification for w3ctag/design-reviews#140 noticed was that the specification had no complete examples (i.e., including how to use worklet code). I think this is both an obstacle to developers trying to understand how the specification works, and to spec reviewers trying to understand how the (new!) worklet stuff actually fits together in a complete example.

It would be helpful if at least one of the examples was complete in terms of showing how to connect worklet script to a document and make it work.