recent projects: cleanup ui (#7528)

As the ui for the file finder was recently changed in #7364, I think it
makes sense to also update the ui of the recent projects overlay.

Before:

![image](https://github.com/zed-industries/zed/assets/53836821/8a0f5bef-9b37-40f3-a974-9dfd7833cc71)

After:

![image](https://github.com/zed-industries/zed/assets/53836821/7e9f934a-1ac3-4716-b7b6-67a7435f3bde)


Release Notes:

- Improved UI of recent project overlay