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da43067b - Preserve selected feature tab in Performance page exports (#9861)

Preserve selected feature tab in Performance page exports (#9861) * Preserve selected feature tab in Performance page exports The Performance page tracked the selected feature tab via `selectedFeatureTabIndex`, but it was never persisted to offline exports, so loading exported data always reset to the first tab. Mirror the Memory page's existing behavior: serialize the selected tab index into `OfflinePerformanceData` and restore it when loading offline data so the user lands on the tab they exported from. Closes #5150 * Honor and clamp the restored tab index when loading offline data Address review feedback on the offline tab restoration: - The restored selectedFeatureTabIndex was immediately reset to 0 by the default-feature activation in TabbedPerformanceView. Use the restored index (clamped to the available tabs) when activating the default feature instead of hardcoding 0. - The number of visible tabs can be smaller when loading offline data than when it was exported, so an out-of-range index could be passed to AnalyticsTabbedView. Clamp the index passed as initialSelectedIndex. - Add a round-trip test for a non-zero selectedTab. * Add release note for performance export tab fix