Update SharedArrayBuffer tests to account for COOP/COEP

[annevk]

This relates to whatwg/html#4734. I figured I'd create a tracking issue to document some decisions.

• css/: CSS and SharedArrayBuffer: don't make support conditional #17689 (cleanup, not blocking)
• html/:
  • HTML: cleanup [[CanBlock]] tests #17688 (cleanup)
  • Add optional test for cloning of error stacks #17159 (initial infrastructure cleanup by @domenic)
  • HTML: BroadcastChannel and SharedArrayBuffer success case revamp #17760
  • HTML: SharedArrayBuffer infrastructure adjustments #17761
• orientation-sensor/ & portals/: Orientation/Portals: make SharedArrayBuffer non-optional #17720 (cleanup)
• wasm/: Not touching these as they use the jsshell global which is not standardized.
• webaudio/: Web Audio: SharedArrayBuffer and COOP/COEP #17719 (assumed that we'll inherit COEP into worklets without a worklet having to declare it)

(I'll edit OP as I go, feel free to reach out if you want to help.)

[annevk]

The main thing left here is adding tests to ensure postMessage() throws when COOP/COEP isn't there.

cc @csreis

[annevk]

That's #17802. I think this is done, apart from getting things reviewed.

[annevk]

This and more is now tracked by whatwg/html#4734 (apart from the CSS cleanup PR, which isn't important). Closing this.