Add a JS copy text utility.

[cycomachead]

Is your feature request related to a problem? Please describe.
We should be able to make it easy for people to copy relevant (non-code) text.

Describe the solution you'd like
Add a class .js-copy-text or something to any HTML element. Floating next to the text a little copy icon should appear which grabs the textContent of the HTML element.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
The action should be keyboard accessible.