Fix setTimeout() when there's no active script

[domenic]

Closes #9633.

• At least two implementers are interested (and none opposed):
  • Firefox already behaves this way
  • Chrome is interested in updating at least this far
• Tests are written and can be reviewed and commented upon at:
  • Test import() + nested setTimeout() web-platform-tests/wpt#41895
• Implementation bugs are filed:
  • Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=1133238
  • Gecko: N/A
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=261377
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): N/A because no base URL concept, I believe
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): N/A because no base URL concept, I believe
• MDN issue is filed: N/A, edge case

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

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/timers-and-user-prompts.html ( diff )

[domenic]

@bathos and/or @Lubrsi, if you have time to check this out, please take a look!

[bathos]

Looks right to me!

[hiroshige-g]

Looks good.

The current Chromium's behavior is actually "always no active script", so as for "no active script" case, no fix is needed.

https://bugs.chromium.org/p/chromium/issues/detail?id=1133238 listed is actually about fixing "with active script" case.

[Lubrsi]

LGTM! Fixes SerenityOS/serenity#20970, implementation can be found here: SerenityOS/serenity#21051