Remove "locked for focus"

[domenic]

This was never implemented in WebKit or Chromium, and only partially implemnted in Gecko.

Closes #11177.

• At least two implementers are interested (and none opposed):
  • WebKit and Chromium reportedly don't implement
  • Gecko is interested in removing per Webkit/Blink/Gecko don't seem to implement locked for focus correctly #11177.
• Tests are written and can be reviewed and commented upon at:
  • TODO @sefeng211
• Implementation bugs are filed:
  • Chromium: N/A
  • Gecko: TODO @sefeng211
  • WebKit: N/A
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): N/A
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): N/A
• Corresponding HTML AAM & ARIA in HTML issues & PRs: N/A
• MDN issue is filed: I checked that https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/focus doesn't go into this level of detail, so N/A
• The top of this comment includes a clear commit message to use.

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

[sefeng211]

(sorry didn't get a chance to write the tests this week, will do it next week)