Bugfix FXIOS-29046 [Tab Tray] Fix delay when executing “Close All Tabs” action

[Aniket-pd]

📜 Tickets

Jira ticket
Github issue

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💡 Description

Documented how the bulk close-all path updates the in-memory tab list immediately, defers web-view teardown, and recalculates selection only once to keep the UI responsive while still issuing delegate notifications.

Summary

• Snapshot all tabs in the selected mode and remove them in one pass.
• Defer heavy teardown work (downloads, web views, delegate calls) to the next run loop so the UI stays responsive.
• Recalculate selection only once,pick the most recent surviving tab or create a new one if needed.
• Preserve prior selection when possible to avoid sluggishness from repeated recalculations.
• Snapshot delegates before async teardown to ensure all receive removal and close-all notifications.
• Eliminate redundant synchronous callbacks for cleaner and faster behavior.

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📝 Checklist

• I filled in the ticket numbers and a description of my work
• I updated the PR name to follow our PR naming guidelines
• I ensured unit tests pass and wrote tests for new code
• If working on UI, I checked and implemented accessibility (Dynamic Text and VoiceOver)
• If adding telemetry, I read the data stewardship requirements and will request a data review
• If adding or modifying strings, I read the guidelines and will request a string review from l10n
• If needed, I updated documentation and added comments to complex code