Add `convert to {upper,lower} case` commands (#2824)

Release Notes:

- Added `convert to upper case` and `convert to lower case` commands
([#1011](https://github.com/zed-industries/community/issues/1011)).
5c2f38a0bcJoseph T. Lyons committed on 8/4/2023, 10:12:55 PM· committed by GitHubparentsd3c19668c98b02
2 files changedLine totals unavailable