feat(core): enhance org-insert-link, add completion for `~/` prefix.

[PannenetsF]

Hi guys, I am trying to hack for ~/ prefixs.

Even if the cmp is configured with org-mode and path sources, the <space>oli cannot auto-complete the ~/ prefix. Also, this issue is the same at emacs org-mode.

It is useful as I have multiple machines to sync with. I set my org folder as ~/org/, but the ~ can be

1. private macOS: /User/pf/
2. Working Linux: /home/pf/
3. ...

Any suggestion is appreciated. :)