Fixes
https://linear.app/zed-industries/issue/Z-1812/find-in-terminal-panel-is-broken

![CleanShot 2023-05-25 at 15 18
01@2x](https://github.com/zed-industries/zed/assets/482957/ddb33b61-d253-4de1-961f-14b24aaa3e46)

This also removes navigation controls from the terminal panel, given
that terminals don't make use of that feature anyway. When the toolbar
is empty, we'll avoid showing it altogether.

![CleanShot 2023-05-25 at 15 17
26@2x](https://github.com/zed-industries/zed/assets/482957/52419f2c-bca0-494a-a9b3-88e183b4c12f)


Release Notes:

- Fixed a regression that was preventing the terminal panel from being
searched.