Wrap "activate view transition" with script prepare/clean up

[noamr]

This ensures that we perform a microtask checkpoint (and set the incumbent script) right after resolving/rejecting the ViewTransition promises.

It's necessary as those promises need to be resolved before the other rendering operations, mainly style/layout.

• [ ] At least two implementers are interested (and none opposed):
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• [ ] Tests are written and can be reviewed and commented upon at:
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• [ ] Implementation bugs are filed:
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  • 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): …
• [ ] MDN issue is filed: …
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/browsing-the-web.html ( diff )

[khushalsagar]

Thanks. LGTM!

[noamr]

@domenic I applied the nit suggestions and also filled in the boxes. Ready to merge?