Select buffer search query on follow-up cmd-f (#10745)

https://github.com/zed-industries/zed/assets/2690773/fd754cfc-aca5-4c4d-9b42-53d1c8eca0e9

Unfortunately, the tests did not work for me, as the `FocusSearch`
action handlers were never called for me.

Release Notes:

- Improved buffer search workflow: follow-up cmd-f select query string