Revise show markup & copy experience

[scottaohara]

I would expect the show markup buttons to act more like toggle buttons rather than their current experience of revealing the markup, but you then can't close it.

When the markup pattern opens, focus doesn't get updated to the new copy button, or get sent to the code pattern.

When the copy button is activated, a "copied" message is visually shown, but not announced. Depending on the screen reader, the code that was revealed may start getting announced (VO) or nothing will be announced (JAWS).