src/vs/workbench/browser/parts/editor/tabsTitleControl.ts/TabsTitleControl/isMoveOperation
class TabsTitleControl:	private isMoveOperation(e: DragEvent, sourceGroup: GroupIdentifier, sourceEditor?: EditorInput) {
		if (sourceEditor?.hasCapability(EditorInputCapabilities.Singleton)) {
			return true; // Singleton editors cannot be split
		}

		const isCopy = (e.ctrlKey && !isMacintosh) || (e.altKey && isMacintosh);

		return !isCopy || sourceGroup === this.group.id;
	}