Use clippie module to copy to clipboard (#23801)

Externalize clipboard copying to the
[clippie](https://github.com/silverwind/clippie) module which I feel I
can maintain outside this repo for shared benefit with my other
projects.

The module is feature-equivalent to the previous code and has one
improvement where it sets `aria-hidden` on the fallback textarea,
preventing screen readers from picking it up. Also it support `Array` of
`content` as well to copy multiple items at once, in case it's ever
needed.

package.json

@@ -19,6 +19,7 @@
     "add-asset-webpack-plugin": "2.0.1",
     "ansi-to-html": "0.7.2",
     "asciinema-player": "3.2.0",
+    "clippie": "3.1.4",
     "css-loader": "6.7.3",
     "dropzone": "6.0.0-beta.2",
     "easymde": "2.18.0",