Add synced tabs persistence

[HiDeoo]

Closes #1851 and follow-up to #953.

This PR adds persistence to the synced tabs feature by relying on localStorage to store the synced tabs state.

This pull request is still a draft for 2 reasons:

• There seems to be a flash of invalid tab that can randomly happen once in a while in development mode. I'd like to investigate this further and see if we can avoid it.
• I want to play a bit more with the feature as most of the time so far has been spent on when/how to include the script to restore the synced tabs rather than actually using the feature.

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Latest commit: ed1b3bf

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[HiDeoo]

Undrafting this PR as I would like to get more eyes on it and have some people play with the changes, maybe during a T&D session or something similar.

The flash of invalid tabs that I mentioned is randomly present but only during dev like I mentioned and I'm not sure there is a reliable way to remove it. In production tho, I've never seen it but that's why I would like to have more people test it.

There is also probably room for improvements in the inline script but that could be done later on when we confirm that the current approach is working as expected.

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[delucis]

Getting an early review in before we go through this on T&D on Thursday. Working great in the deploy preview for me @HiDeoo!

[delucis]

LGTM from an initial review! Look forward to seeing how testing goes tomorrow.

[HiDeoo]

Based on the feedback during the T&D exploration, I've updated the PR:

• We're now using a global symbol to keep track in Astro.locals if the restore script has been rendered or not. The goal is to avoid potential clash with user-defined variables in Astro.locals (even if unlikely).
• I tried quite a few scenarios (embedded components, delayed components, etc.) to see if we could hit any issue with the restore script. So far, everything seems to work as expected no matter the scenario.

[delucis]

LGTM! Left two nits, but don’t have any “real” comments left!

[delucis]

Nit, but I think tabs will always be set here given it is declared as [...query]:

Suggested change

	tabs?.[0]?.setAttribute('aria-selected', 'false');
	tabs?.[0]?.setAttribute('tabindex', '-1');
	tabs[0]?.setAttribute('aria-selected', 'false');
	tabs[0]?.setAttribute('tabindex', '-1');