Generate scraped examples buttons in JS Follow-up of https://github.com/rust-lang/rust/pull/129796. To reduce the page size when there are scraped examples, we can generate their buttons in JS since they require JS to work in any case. There should be no changes in display or in functionality. You can test it [here](https://rustdoc.crud.net/imperio/gen-scraped-buttons/doc/scrape_examples/fn.test.html). cc `@willcrichton` r? `@notriddle`