Maybe support draggable in PostPicker component

Hi HM family!

We were using the [PostPicker](https://github.com/humanmade/block-editor-components/blob/main/src/components/PostPicker/index.js#L117) component recently and we had some manually re-ordering to do. The `reOrderUp/Down` features work **really well ❤** - but I'd love to be able to drag and drop items to control the ordering.

Absolutely all good, if this isn't on the roadmap - if we need it quicker, we'll patch upstream for y'all - but it's a low priority enhancement for us.

All the best y'all 👋 🙇 💯 🎉