Request: text editing icons
I have a few icons to request, some of which I think are mandatory for icons libraries.

- Bold
- Italic
- Underline
- Strikethrough/Line through

- arrow-line-middle-vertical
- arrow-line-middle-horizontal

![image](https://user-images.githubusercontent.com/1667234/99006937-f58a5700-258e-11eb-95aa-e3591f8fb356.png)

_Originally posted by @RichardBarrett in https://github.com/phosphor-icons/phosphor-home/issues/7#issuecomment-726395166_