No issue: Enable the tabs tray refactor in nightly

[jonalmeida]

We have our core functionality in now, so we can enable this on nightly for folks to test.

There are some known issues that we should fix before we let this ride the trains though.

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

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[jonalmeida]

For the performance team: opening the tabs tray does not touch cold or warm boot code, so should not affect startup perf.

[rocketsroger]

🚀