This commit introduces the UI model for the 'view in playground' feature.
The option is a 1-click UX if only one playground link has been configured
for the programming language in the code block. If multiple such playgounds
have been configured, we display a popover with the different playground
options.
The actual code extraction logic occurs here and we set the target href
combining the url_prefix and the extracted code for both these scenarios.
Fixes: #11618
Anders Kaseorg
Sumanth V Rao