[clipboard-apis] integrate "integration with rich text editing apis" into cut/copy/paste actions (#18)

It's a bit confusing to have this stuff separate at the end of the spec:
https://w3c.github.io/clipboard-apis/#integration-with-rich-text-editing-apis

We should probably just drop that section and add relevant steps to the actions.

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/clipboard-apis/issues/18