Update prompt library styles (#12689)

- Extend Picker to allow passing a custom editor. This allows creating a
custom styled input.
- Updates various picker styles

Before:

![CleanShot 2024-06-05 at 22 08
36@2x](https://github.com/zed-industries/zed/assets/1714999/96bc62c6-839d-405b-b030-31491aab8710)

After:

![CleanShot 2024-06-05 at 22 09
15@2x](https://github.com/zed-industries/zed/assets/1714999/a4938885-e825-4880-955e-f3f47c81e1e3)

Release Notes:

- N/A