Re-reveal reference selection in peek preview on repeat tree click

[Copilot]

In the Go to References zone widget, clicking an already-selected item in the references tree was a no-op. If the user had scrolled the preview editor away from the highlighted reference, there was no way to bring it back into view short of selecting a different reference first.

Changes

• referencesWidget.ts — In ReferenceWidget._revealReference, the early-return on this._revealedReference === reference previously short-circuited all work. It now re-applies the selection and re-centers the range in the preview editor on repeat clicks, while still skipping the expensive work (model resolution, title update, tree reveal) since that state is already correct.

if (this._revealedReference === reference) {
    const model = this._preview.getModel();
    if (model) {
        const sel = Range.lift(reference.range).collapseToStart();
        this._preview.setSelection(sel);
        this._preview.revealRangeInCenter(sel, ScrollType.Smooth);
    }
    return;
}

The new path mirrors the existing first-reveal logic (setSelection + revealRangeInCenter) and uses ScrollType.Smooth since the preview model is unchanged.