Superscript & Subscript
**Describe the requested icon**
I would like to have a superscript and subscript icon.
Phosphor already covers almost every symbol that you need for an text editor, but those icons are missing.
A generic icon like the one shown in my screenshot could also be used for mathematical applications.

**Screenshots**
![screenshot 2023-04-09 at 23 01 33@2x](https://user-images.githubusercontent.com/45072099/230796412-9feffd37-dd65-4379-aaaa-48b7fce1346d.jpg)
