Only swap Alt-hold close action for the hovered tab in MultiEditorTabsControl

[Copilot]

Holding Alt in MultiEditorTabsControl swapped the per-tab close action into "Close Others" for every tab in the group at once, which is visually noisy since only one tab can actually be clicked.

Changes

• Hover-aware state: replaced the control-wide wantsCloseOthersAction: boolean with hoveredTabIndex: number | undefined, tracking which single tab the mouse is currently over.
• Hover tracking: added mouseenter/mouseleave listeners on each tab (in registerTabListeners) that update hoveredTabIndex via a new setHoveredTab() method.
• Swap condition: redrawTabAction() now swaps Close → Close Others only when altKey is held and the tab being redrawn matches hoveredTabIndex. Unpin behavior is unaffected.
• Targeted redraws: Alt press/release and hover changes now redraw only the affected tab(s) (previous + new hovered tab) instead of iterating over all tabs via forEachTab.
• Stale state cleanup: hover is cleared when the mouse leaves the tabs container, and when the tab count shrinks below the hovered index after closing tabs (handleClosedEditors), preventing a tab from getting stuck showing "Close Others".

// Before: applies to all tabs
const wantsCloseOthersAction = hasCloseAction && this.wantsCloseOthersAction;

// After: only the hovered tab
const wantsCloseOthersAction = hasCloseAction && modifierKeyEmitter.keyStatus.altKey && tabIndex === this.hoveredTabIndex;

[Copilot]

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