assistant2: Add create buffer tool (#11219)

This PR adds a new tool to the `assistant2` crate that allows the
assistant to create a new buffer with some content.

Release Notes:

- N/A

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Co-authored-by: Nathan <nathan@zed.dev>
d01428e69cMarshall Bowers committed on 4/30/2024, 5:43:25 PM· committed by GitHubparentada2791
10 files changedLine totals unavailable