Provide alternative for reordering items without dragging with mouse

Currently there is no keyboard accessible alternative for reordering the task items which prevents assistive technology/ keyboard-only users from accessing the feature.

A number of implementations I've seen like [this example from salesforce-ux][1] enable user to press `SPACE` to move an item around with arrow keys and `SPACE` to place an item. Something to keep in mind for this element is making sure to not interrupt checking of checkbox (which can also be done `SPACE`).

Other references:

[Upcoming WCAG change 2.5.7 Dragging Movements (AA)](https://www.w3.org/WAI/standards-guidelines/wcag/new-in-22/#257-dragging-movements-aa)

[4 major patterns for accessible drag and drop](https://medium.com/salesforce-ux/4-major-patterns-for-accessible-drag-and-drop-1d43f64ebf09)

[1]: https://salesforce-ux.github.io/dnd-a11y-patterns/#/sortB?_k=1lp55f

issue 中沒有指定檔案或測試。先找出工作清單拖放和項目重新排序的進入點，接著檢查鍵盤焦點和核取方塊啟用的運作方式。當僅使用鍵盤的使用者和輔助技術使用者可以不必拖曳就重新排序項目，同時 SPACE 仍支援核取方塊互動時，即表示完成。

由索引模型根據 Issue 內容生成。