Trim index output (#11445)

Trims down the project index output view in assistant2 to just list the
filenames and hideaway the query.

<img width="374" alt="image"
src="https://github.com/zed-industries/zed/assets/836375/8603e3cf-9fdc-4661-bc45-1d87621a006f">

Introduces a way for tools to render running.

Release Notes:

- N/A

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Co-authored-by: Max <max@zed.dev>