Update the contents of the select fallback button text element - #13146

Use string replace all to update the select fallback button text element with the selected option text.

The rendering section defines select fallback button text as a div element. The existing step assigns the string directly to the element reference instead of updating its contents.

Spec: https://html.spec.whatwg.org/multipage/form-elements.html#clone-selected-option-into-select-button

• At least two implementers are interested (and none opposed):
  • …
  • …
• Tests are written and can be reviewed and commented upon at:
  • …
• Implementation bugs are filed:
  • Chromium: …
  • Gecko: …
  • WebKit: …
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): …
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): …
• Corresponding HTML AAM & ARIA in HTML issues & PRs:
• MDN issue is filed: …
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)