Add copy to clipboard button to code blocks

[aaronshekey]

A suggestion from @MaxHorstmann that I'd love to include at some point. Code blocks could use their own copy to clipboard button.

There have been other requests for a proper stimulus copy to clipboard button, so perhaps we could break this down a bit and combine the components where necessary?

[b-kelly]

Considering Stimulus's tutorial component is literally a "copy to clipboard" component, I feel like this feature is attainable.

[MaxHorstmann]

Top post on r/ProgrammerHumor today:

https://www.reddit.com/r/ProgrammerHumor/comments/192bngn/backtostackoverflowagain/

Come on, friends, give us a "copy to clipboard" button! <3